Introduction to Trinitarian Theology

For years at Unam Sanctam Catholicam we have been offering high quality RCIA lesson plans and Power Points that are orthodox and in continuity with the Church's great Tradition. In honor of Trinity Sunday, in which the supreme mystery of the Christian faith is celebrated in awe-filled reverence, we have taken our lesson plan on the Holy Trinity and turned it into a regular article. We have done this for two reasons: first, many Christians, though able to state correctly that the Trinity is one God existing in three divine Persons, may know little more Trinitarian theology than this basic formula. Second, we want to provide an opportunity for people to see an example of the layout and content of one of our lesson plans.

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And now, our lesson on the Most Holy Trinity.

The Holy Trinity

“Going therefore, teach ye all nations; baptizing them in the name of the Father, and of the Son, and of the Holy Ghost.”

-Matt. 28:19

 "I have attempted not so much to speak with authority of things that I know, as to seek to know them by speaking about them with reverence.”

                              -St. Augustine, De Trinitate, I v. 8

The Central Mystery of the Christian Faith

The Holy Trinity is the central mystery of the Christian faith, the truth from which all other truths proceed. The sending of the Son of God by the Father for the redemption of mankind and the indwelling of the Spirit in individual Christians (and in the Church corporately) are not understandable apart from the truth that God is One Divine Being existing in Three Persons: the Father, the Son and Holy Spirit. This truth, then, is the fundamental revelation of the New Covenant, the highest doctrine in the hierarchy of revealed truth and the basic, distinctive characteristic of traditional, historic Christianity.

 Mystery of the Trinity

In theology, the Trinity is said to be a mystery. According to the First Vatican Council, a mystery is a truth which we are not merely incapable of discovering apart from Divine Revelation, but which, even when revealed, remains "hidden by the veil of faith and enveloped, so to speak, by a kind of darkness" (Dogmatic Constitution on the Catholic Faith, 4). It does not contradict reason, but goes beyond it. Thus, even though the mystery of the Trinity may be rational and coherent, it cannot fully be grasped by our understanding; part of it will always remain mysterious. The Trinity, since it pertains to the very life of God Himself, is the central mystery of the Christian faith (CCC 261).

Nevertheless, we can use analogies and figures to help us understand this mystery. However, even if certain analogies help us to better understand what God is, we have to remember the teaching of the Fourth Lateran Council, that “between creator and creature there can be noted no similarity so great that a greater dissimilarity cannot be seen between them” (Constitutions of Lateran IV, 2). Ultimately, because God is utterly unique, any analogy we invent to describe Him will fall far short of His reality.

Thus, humility is always needed when speaking of the Trinity, for we speak of the very life and being of God Himself.

The Trinity In Scripture

The Trinity is not formally defined or explained in Scripture; however, Christians have always seen the Trinity taught implicitly in several biblical passages. For example, John 1:1, in which it states: “In the beginning was the Word, and the Word was with God, and the Word was God.” This passage clearly states that the Word of God, while being God Himself, is also “with God.” Many other passages have been brought forward that support the Church’s traditional Trinitarian approach:

Gen. 1:26
Gen. 16:7-13
Ex. 3:2-14
Ps. 2:7
Ps. 110
Prov. 8
Wis. 7-8
Isa. 11:2
Ezk. 11:5
Matt. 28:19
Luke 3:22
John 8:58
John 10:33
2 Cor. 13:14
Eph, 4:4-6
Php. 2:1-2
Php. 2:9-11
1 John 5:7

Dogmatic Definitions

The Church has dogmatically defined the mystery of the Trinity many times. From the most ancient days of Christianity, Trinitarian faith was expressed in the Apostles’ Creed; the Didache (c. 70 AD) says baptism was administered “in the name of the Father, and of the Son, and of the Holy Spirit.”

The most famous definition was at the Council of Nicaea (325), whose definition was meant as explaining the equality of the Father with the Son. The Nicene Creed, which we recite at Sunday Masses, states that the Son is “the only Son of God, eternally begotten of the Father, God from God, light from light, true God from true God, begotten, not made, consubstantial with the Father.”

The Nicene definition was restated at the Council of Constantinople (381) and further defined at the subsequent regional councils at Toledo in the 5th-7th centuries, which were aimed at defining the orthodox Faith against the Arians, who denied the equality of the Father with the Son.

The Creed of St. Athanasius, also called to Quicumque Vult, was the most common formulation of Trinitarian faith used in the Middle Ages. It stated:

And the catholic faith is this: That we worship one God in Trinity, and Trinity in Unity; Neither confounding the Persons; nor dividing the Essence. For there is one Person of the Father; another of the Son; and another of the Holy Ghost. But the Godhead of the Father, of the Son, and of the Holy Ghost, is all one; the Glory equal, the Majesty coeternal. Such as the Father is; such is the Son; and such is the Holy Ghost. The Father uncreated; the Son uncreated; and the Holy Ghost uncreated. The Father unlimited; the Son unlimited; and the Holy Ghost unlimited. The Father eternal; the Son eternal; and the Holy Ghost eternal. And yet they are not three eternals; but one eternal. As also there are not three uncreated; nor three infinites, but one uncreated; and one infinite.”

So we see that from the patristic era going into the Middle Ages, a standard formulation of the Trinity as one God in Three Persons was common. This formulation would be restated at subsequent Councils right up to the Second Vatican Council. The Catechism of the Catholic Church’s teaching on the Trinity can be found in paragraphs 232-267. It states that:

The mystery of the Most Holy Trinity is the central mystery of Christian faith and life. It is the mystery of God in himself. It is therefore the source of all the other mysteries of faith, the light that enlightens them. It is the most fundamental and essential teaching in the "hierarchy of the truths of faith". The whole history of salvation is identical with the history of the way and the means by which the one true God, Father, Son and Holy Spirit, reveals himself to men "and reconciles and unites with himself those who turn away from sin" (234). 


Nature and Person

A helpful distinction to make when evaluating the doctrine of the Trinity is to understand the difference between nature and person. The nature of something corresponds to the questions “What is it?” Person, on the other hand, answers the question, “Who is it?” In the world, everything has a nature, that is, it is something, though only rational creatures also have personhood. So, in the example of a human person:

Nature: What Are You?    >>>    I am a human being.

Person: Who Are You?     >>>    I am Bob Smith.

We can see that the terms “human being” and “Bob Smith” have a close relation; without doubt, Bob Smith is a human being, and he could not be otherwise. But to be a human being is not the same thing as to be Bob Smith.

If we relate this to the Trinity, we see that the nature of God (what He is) is Divinity, or the Divine Nature.; i.e., God. God’s nature is God, or as He said to Moses, “I am that I am.” But who God is corresponds to the question of personhood. And in the case of God, He is three divine Persons: the Father, the Son and the Holy Spirit. So, in the Trinity:

Nature: What is God?   >>>   God is God; He possesses a single Divine Nature

Person: Who
is God?    >>>   God is Father, Son and Holy Spirit, three  divine Persons

This brings us back to the classical example of the Trinity, which defines God as Three Persons who share one Divine Nature. The question is really not how one can be three and three can be one, but how one Being can consist of Three Persons and each Person be God whole and entire. In the case of humans, three persons can certainly share one nature (Peter, Paul and Mary are three persons, and they all share a common human nature); the difference between humans and God is that, in the first case, the three humans who share the one nature are also three distinct beings, and no one person possesses the entirety of human nature in himself; yet in the case of God, the Three Divine Persons possess one common nature but nevertheless remain one Being and each Person themselves possesses the fullness of the Divine Nature.

This is the true mystery of the Trinitarian life, for unlike human beings, the Persons of the Trinity do not “share” the divine nature, but each Person is God, whole and entire. The Catechism teaches:

“The Trinity is One. We do not confess three Gods, but one God in three persons, the “consubstantial Trinity.” The divine persons do not share the one divinity among themselves but each of them is God whole and entire: “The Father is that which the Son is, the Son is that which the Father is, the Father and the Son that which the Holy Spirit is, i.e., but nature one God.” In the words of the Fourth Lateran Council (1215): “Each of the persons is that supreme reality, viz. the divine substance, essence or nature.” (CCC 253)


The Nature of God

Nature is what something is. Thus, when we come to speak of the nature of God, we are attempting to say just what, exactly, God is.

It is very difficult to say with precision what the nature or essence of God consists of, since He is absolutely unique and by definition beyond our ability to fully comprehend by reason alone. Nevertheless, Christian Tradition has affirmed several things about God’s nature:

Simplicity/Unity: God is not made up of any composite parts; His nature is utterly and completely simple. God has no Body. This also refers to understanding His attributes, which are all one in His essence; thus, His justice is not different than His mercy, etc. The Three Persons of the Trinity do not constitute different “parts” that added together make God as a sum.

Goodness: God is pre-eminently good, and is Himself the source of all goodness and is everything that is desirable. Are other things are good and desirable only insofar as they partake in His goodness.

Perfection: God Himself is the perfection of all virtue and every desirable attribute and is at the same time the source of perfection in creatures as well. A creature is perfect to the degree that it is like God. There is no imperfection in God.

Infinity: God is not bounded by anything, neither in His ability to act (omnipotence), nor His ability to be present at each and every place and time in His creation (omnipresence) nor His ability to have perfect knowledge of all things (omniscience). God is not bounded by anything. It should be noted that the fact that God “cannot” lie or commit evil does not bound God. To lie or commit sin is to reduce oneself, to fall away from Being and Goodness towards non-being and imperfection. It is precisely because God is infinite and perfect that He cannot sin, for to do so would be to bind Him by introducing a negation into His being. We thus recall the fundamental truth that sin and evil are negations to being and add nothing to it ontologically.

Immutability: Because God is perfect and is utterly simple, He needs no movement of change to improve His happiness or obtain anything He lacks. Therefore His essence is changeless and immutable. Note this does not mean that God cannot feel or experience emotion, but it does mean that He is not moved or changed in His nature or affected by anything external to Himself.

Eternity: God has no beginning and no end. He is not bound by time, which is related to His infinitude. God Himself is the source of time; God has always existed and will always exist.

Existence: Finally, the Scholastic theologians (most notably St. Thomas Aquinas) identified God’s nature with the act of existence itself. In all other things, essence and existence are distinct; my essence (what I am) is distinct from my act of existing; to be human is not the same thing as to exist. I am a human who exists. Yet in God, posited St. Thomas, the very act of existing is His essence; God is a being whose very nature is to exist. This gives a rich, philosophical meaning to God’s reference of Himself as “I am that I am” in Exodus 3:14. Thus, in God, there is no real distinction between essence and existence.

Distinction and Relativity

Despite the absolute oneness of the Godhead, the Persons of the Trinity are nevertheless truly distinct. Father, Son and Holy Spirit are not just three ways of talking about the same thing, nor are they three different manifestations of God – they are truly distinct from one another. God is one, but He is not solitary. The true distinctions between the Persons reside in their relations to one another, their relativity. The eleventh Council of Toledo (c. 675) formulated the teaching this way:

“In the relational names of the Persons the Father is related to the Son, the Son to the Father, and the Holy Spirit to both. While they are called three persons in view of their relations, we believe in one nature or substance.”

The Father is the foundational principle of the Trinity. From the Father the Son is begotten, and the Son stands in relation to the Father as generated to generator. The Spirit is not begotten but proceeds (or is “spirated”) from both the Father and the Son. The distinction between the Son being begotten and the procession of the Spirit is to preserve the truth that the Son and the Spirit come from the Father in different ways; the Son alone in said to be “begotten” while the Spirit’s procession is called spiration.

Mutual Indwelling

The unity and distinction of the Three Persons is resolved in their mutual indwelling. The three Persons of the Trinity mutually indwell each other in such a way that they are each with and in the other in the fullest possible sense. In John 1, the Word is “with God” and at the same time “is God.” The persons of the Trinity "reciprocally contain one another, so that one permanently envelopes and is permanently enveloped by, the other whom he yet envelops". (Hilary of Poitiers, Concerning the Trinity 3:1)

Ontological and Economic

Theologians distinguish two different modes of speaking about the Trinity; thus the distinction between the ontological or theological Trinity and the economic Trinity. The term “ontological Trinity” refers to the interior life of the Trinity—the reciprocal relationships of Father, Son, and Spirit to each other without reference to God's relationship with creation. It is God as He exists in Himself.

The “economic Trinity”, on the other hand, refers to the acts of the Persons of the Trinity in their relationship to the economy of Creation. The creation of the world, sending of the prophets, coming of the Messiah with His atoning death, the sending of the Spirit and establishment of the historical Church are all predicated of the economic Trinity, as is the acts of God in the lives of the individual members of the Church.

Appropriation and Trinitarian Works

In theology, the term appropriation is used in speaking of the different Persons of the Trinity. It consists in attributing certain names, qualities, or operations to one of the Persons, not, however, to the exclusion of the others, but in preference to the others. The qualities and names thus appropriated belong essentially to all the Persons; yet, according to our understanding of the data of revelation and our theological concepts, we consider some of these characteristics or names as belonging to one Person rather than to another, or as determining more clearly this particular Person.

For example, causality is typically attributed to the Father, the organization of secondary causes to the Son, and the preservation and final consummation of things to the Spirit; yet, in an absolute sense, each Person of the Trinity is responsible for each. This is true of the Names for the Three Persons as well; “God” typically refers to the Father, “Lord” to the Son, and “Spirit” to the Holy Spirit, even though each Person of the Trinity if God, Lord and Spirit.[1] The term “the Almighty” is usually spoken with reference to the Father, but in fact each of the Persons is rightfully said to be Almighty.

The terms we use in appropriating certain traits to the Persons are not arbitrary; they are taken from the data of Scripture and are fitting to use because of the analogical nature of man’s understanding of the Trinity. For example, Scripture itself associates the Holy Spirit with the preservation of Creation: when you take away their breath, they die and return to the dust.

"When you send your Spirit,
they are created” (Ps. 104:29-30); yet we know that the preservation of Creation is a work of all Three Persons of the Holy Trinity. Therefore, the various ways we speak of the Persons are informed by Divine Revelation.

While we can use the language of appropriation to speak of the attributes of God, we can also use it to discuss His works. For example, God the Father is often associated with the creation of the world, God the Son with its redemption, and God the Spirit with the sanctification of God’s people, and the Three Persons are sometimes referred to respectively as the Creator, Redeemer and Sanctifier. Nevertheless, even though it is proper to speak of the Persons by these titles, the work of each Person is common to the Trinity; each of the Three Persons was involved in the creation of the world, each Person was integral in its Redemption, and each Person can be said to sanctify God’s people. But, again, by way of analogy grounded in the words of Scripture, we appropriate certain actions to certain Persons even though these works of the Trinity are done in common.

Trinitarian Missions

That being said, there are certain special acts of God that are proper to each of the Three Persons in a unique sense. These are not done in common by the Trinity but can be said only of one Person in particular. These special acts are referred to as the Trinitarian missions and are distinguished by their uniqueness and their central role in the economy of salvation.

The mission of the Father in the economy of salvation is the sending of the Son. The Spirit did not send the Son, nor does the Son send Himself. This mission is only properly spoken of with reference to the Father alone.

The Son’s mission is to be begotten of the Father and Incarnate as a true Man on this earth. Only the Son was Incarnate; the Father was not Incarnate, nor the Spirit, but the Son alone.

The Spirit proceeds from the Father and the Son and is sent to the Church, in such a way that He is the soul of the Church, as popes Leo XIII and Pius XII taught. Only the Spirit was sent to the Church in such as to be its soul of the Church; neither the Father nor the Son was sent to the Church or is the soul of the Church.

These special missions of the Trinitarian Persons all pertain to the economy of salvation, the plan of God for the redemption of mankind.

Generation and Procession

The Trinitarian missions are related to the processions of the Persons within the Godhead. There are two processions within the Trinity (by procession is meant the origin of one from another). These two processions are the begetting of the Son by the Father and the procession or “spiration” of the Holy Spirit from the Father and the Son. Because we are referring to processions within the Trinity, we are referring to the theological or ontological Trinity, whose processions are internal and eternal – that is, though the Son is begotten of the Father and the Spirit proceeds from the Father and the Son, these movements are eternal and do not suggest that the Father is prior to the Son or the Spirit in time, although it does suggest that the Father is the foundational or generating principle within the Trinity. This is why the Father is never said to be begotten.

The appropriate theological vocabulary to express this reality is that the Son alone is generated while the Spirit proceeds. This generation and procession within the theological Trinity are mirrored in the external processions of the Divine Persons through their missions in the world.

Expressing the Trinity by Analogy

As mentioned above, the doctrine of the Trinity is a mystery, which in theological vocabulary means a teaching that, while truly logical and coherent, nevertheless is beyond the pale of our reason to comprehend fully. The doctrine of the Trinity does not contradict reason, but it does go far beyond it. No matter how much we have studied it, prayed about it, or spoke of it, there is still a veil of darkness over it that can only be penetrated by faith.

Because of this fact, Christian saints and theologians have frequently resorted to analogy to describe the Trinity. The most famous analogy was that attributed to St. Patrick, who likened the three leaves of a shamrock to the Three Persons of the Trinity; as the leaves of the shamrock, are distinct while remaining one, so are the Persons three while remaining one Being. More precise was the attempt of St. Augustine, who in the work De Trinitate attempted to understand the Trinity by looking at the operations of the human soul, which is made in God’s image. Augustine liked the Father, the Son and the Holy Spirit to the faculties of Will, Memory and Understanding in a human being – while each faculty is logically distinct, they act as one and are united to one another in such a substantial way that they each depend upon the other. More recently, Anglican author Dorothy Sayers in her book Mind of the Maker (1941) took a novel but intriguing approach to the problem by explaining the relation between the Trinitarian Persons in light of the creative faculties of an author.

Following upon the biblical teaching that “God is love” (1 John 4:8), some have posited the experience of human love as the best analogy. Love requires a lover (Father) a beloved (Son) and the love shared between the two (Holy Spirit). Others have used the example of fire, which consists of a flame, which generates both heat and light; yet though the heat and light proceed from the flame, the three occur together as one phenomenon.

Ultimately, though the analogies are helpful, we must remember that they are only approximations, and no analogy of the Trinity is completely perfect. In the words of Lateran IV, “between creator and creature there can be noted no similarity so great that a greater dissimilarity cannot be seen between them.”

Humility before the Mystery

Ultimately, because the doctrine of the Trinity concerns itself with the very internal life of God, it is incomprehensible to the human intellect. We will spend eternity immersed in the life of the Trinity and in contemplation of God’s majesty and still not come close to exhausting the richness of this mystery.

Nevertheless, the fact that we can never fully comprehend the mystery does not mean that we cannot understand it or say anything positively certain about it. Christ and the Scriptures do give us certain teachings that the Church has always affirmed, understanding that though we can never fully penetrate the depths of this mystery, God nevertheless wills us to know Who He is and that He is Triune. Before this mystery we bow in humility, accepting humbly what God has passed on to us without arrogantly claiming to be able to exhaust its content. Like other mysteries of faith, the Trinity is a truth that goes beyond our reason but does not contradict it. It is incomprehensible, but not illogical. The only proper disposition for reflecting on this truth is humility.

For Further Reading
: St. Augustine, De trintate; Catechism of the Catholic Church, § 232-267, 198-747; Frank Sheed, Theology for Beginners; Pope Pius XII, Mystici Corporis (1943); Pope Leo XIII, Divinum illud munus (1897); Vatican I Dogmatic Constitution on the Catholic Faith; St. Thomas Aquinas, STh, I, Q. 39, art. 1-8; St. Hilary of Poitiers, Concerning the Trinity; Dorothy Sayers, Mind of the Maker (1941).

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[1] With the caveat that, since the Incarnation, the Word of God, which is pure spirit, has been joined to flesh.