Lesson 2: The Existence of the Trinity

Belief in the Trinity is central and crucial to our Catholic faith. Since it is so important, we should try to achieve a better understanding of it.

What the Church believes and proclaims is that in God there are three distinct Persons -- Father, Son and Holy Spirit. Each of the three Persons possesses the one same divine essence or being. So we can say that there is one God in three distinct Persons.

The terms "essence, nature, substance" refer to the divine "being," which is the same for the Father, the Son and the Holy Spirit. The word "Person" refers to the three owners or bearers of the divine being. Thus, what is one in God is the divine being, while what is three in God is the divine Persons. You will note that we are not contradicting ourselves by saying that one is three, since "one" refers to the substance of God, while "three" refers to the Persons. In a future lecture I will give a more detailed explanation of the precise meaning of these theological terms.

For now let it suffice to say that we Catholics believe in the Most Holy Trinity, that is, we believe that there are three Persons in only one God. This profound truth was hinted at in the Old Testament and clearly revealed by Jesus in the New Testament. Before his Ascension into heaven, Jesus sent out his disciples into the whole world and told them to baptize all nations "in the name of the Father, and of the Son, and of the Holy Spirit" (Matt. 28:19). The oldest doctrinal formulation of the Church's belief in the Trinity is the Apostles' Creed which served as the basis of catechetical instruction and as a baptismal confession of faith since the second century. It is based on the Trinitarian formula of Baptism which was just quoted.

The best guide to the Church's belief in the Trinity is found in the Creed. In addition to the Apostles' Creed, there is also the Creed that we say together at each Sunday Mass. This Creed comes from the fourth century and is an excellent summary of our faith: "We believe in one God, the Father, the Almighty, maker of heaven and earth... We believe in one Lord, Jesus Christ, the only Son of God, eternally begotten of the Father, God from God, light from Light, true God from true God, begotten, not made, one in being with the Father....We believe in the Holy Spirit, the Lord, the giver of life, who proceeds from the Father and the Son." This profession of faith proclaims that there is only one God, but also that there are three Persons in the one God.

According to Catholic belief, God is both one and three. If we ask, "What is one in God?", the answer is that he is one in being or substance. If we ask, "What is three in God?", the answer is that there are three "Persons" subsisting in one God.

Some Christian thinkers of the past, confusing what is meant by substance and person, have held that the three divine Persons are distinct individuals like three human beings; thus, they concluded that there are really three gods who work together in some sort of moral unity. Many contemporary Christians apparently have similar views about God. This opinion has often been condemned by Church Councils of the past.

Others have held that God is one Person and one Being, only that he is given three different names in Scripture. These thinkers said that the names, "Father, Son, Holy Spirit," refer to just one Person in the Godhead, namely, the Father. Thus, in their view, the names "Jesus" and "Holy Spirit" are merely other ways of speaking of God the Father. This view has also been condemned as heretical often by the Church. If it were true, it would mean that the Father is Jesus and that the Father died on the Cross on Calvary -- this heresy is called "Patripassionism"; it would mean that the Father did not send his Son to redeem us, but "sent" himself; it would make many of Jesus' statement about the Father and the Holy Spirit either false or unintelligible, such as that he was sent by the Father.

The Fourth Lateran Council in 1215 enunciated the Catholic belief in the Trinity very clearly:

"We firmly believe and profess without qualification that there is only one true God, eternal, immense, unchangeable, incomprehensible, omnipotent, and indescribable, the Father, the Son, and the Holy Spirit: three persons but one essence and a substance or nature that is wholly simple. The Father is from no one; the Son is from the Father only; and the Holy Spirit is from both the Father and the Son equally. God has no beginning; he always is and always will be; the Father is the progenitor, the Son is the begotten, the Holy Spirit is proceeding; they are all one substance, equally great, equally all-powerful, equally eternal; they are the one and only principle of all things -- Creator of all things visible and invisible."

Some of these words and phrases are difficult to understand for one who is not familiar with the teaching on the Trinity. As we proceed I will explain them one by one.


Evidence for the early Church's belief in the Trinity is found in the first creeds as listed at the end of Lesson One.


OLD TESTAMENT: There are hints and suggestions of the reality of the Trinity in the OT.

Look up the following: Gen. 1:26; 3:22; 11:7; Isa. 6:3; 11:2; 61:1- 2; Joel 2:28 (quoted in Luke 4:17 and Acts 2:16ff.); Wis. 9:1-17; Pss. 2:7; 33:6; 110:1; Prov. 8:22-25; Sirach 24:5ff.

NEW TESTAMENT: There are over 40 texts in the NT which mention the three Persons in the Trinity. The main ones are:

-- Matt. 28:19, "...make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit..." In the original Greek the three names are all listed in the same way, indicating equality; so the Son and the Holy Spirit are put on the same level as the Father.

-- Matt. 3:16-17, "And when Jesus had been baptized, just as he came up from the water, suddenly the heavens were opened to him and he saw the Spirit of God descending like a dove and alighting on him. And a voice from heaven said, 'This is my Son, the Beloved, with whom I am well pleased.'" The three Persons are all mentioned in this same passage.

-- 2 Cor. 13:13, "The grace of the Lord Jesus Christ, the love of God, and the communion of the Holy Spirit be with all of you." This verse is used at the beginning of the Novus Ordo Mass and gives expression to the Trinitarian faith.

Reading Assignment

Read what the commentaries have to say about these texts from the OT and NT in reference to the Trinity. You should consult the NEW JEROME BIBLICAL COMMENTARY; and the recently published and excellent INTERNATIONAL BIBLE COMMENTARY edited by Wm. Farmer and published by The Liturgical Press, in Collegeville, Minn. (1998).

Writing Assignment

Write an essay of two or three pages, based on early witnesses, showing that the Church professed belief in three Persons in one God, beginning with the New Testament.


Read Book II of St. Augustine's De Trinitate (On the Holy Trinity).


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