The Most Holy Trinity is not three gods, but One God. The Church teaches that God is Father, Son, and Holy Spirit, three “Persons,” yet one God. Each person is not 1/3 God, but 100% God. Each Person is distinct, yet Father, Son, and Holy Spirit constitute One. We cannot understand how this is possible, because it defies our intellect’s capabilities. As aforementioned, we only know that God is Trinity through Divine Revelation.
One way we know that God is Trinity is because of the myriad evidence in scripture supporting this truth. In the Book of Genesis, God says: “Let us man make man in our image, after our likeness” (Gen 1:26). The plural “our” does not make sense if God were one. However, “the Lord is our God, the Lord alone,” and “there is no God besides” Him (Deut 32:39). Therefore, somehow God is plural yet one. God being Trinity thus seems at least plausible.
In Genesis 18, “the Lord appeared to” Abraham (Gen 18:1). The next verse says that when Abraham looked up, he saw “three men” (Gen 18:1, 2). The three men seem to somehow be or symbolize God, suggesting that the Lord decided to hint at the reality of the Trinity by appearing in the form of three men. Abraham shows these men great hospitality, giving them a “calf, tender and good,” and waiting on them “under the tree while they ate” (Gen 18:8). Abraham’s head-over-heels treatment of these three men suggests that he, a “righteous” man, thinks these men are incredibly important (Gen 15:6).
Moreover, when Abraham sees the men, he calls them “my lord,” not lords (Gen 18:3). In reward for Abraham’s hospitality, the Lord rewards him with a son, and the men tell Abraham that his wife, Sarah, will bear a son in a year’s time. But scripture refers to the men and the Lord in succession, suggesting that they are the same Person/People: “They said to him, ‘Where is Sarah your wife?’ And he said, ‘She is in the tent.’ The Lord said, ‘I will surely return to you in the spring, and Sarah your wife shall have a son’” (Gen 18:9-10).
Elsewhere in Holy Writ, Christ sanctifies the waters of Baptism by humbling Himself to be baptized by St. John the Baptist. When He does so, “the heavens open and the Spirit [descends] upon him like a dove; and [the Father’s] voice [comes] from heaven, ‘Thou art my beloved Son; with thee I am well pleased.’” (Mk 1:10-11).
Throughout the Gospels, Christ claims that the Father has sent Him and that He comes to do the Father’s will (see Jn 4:34, 6:38). In John 17, before He enters His Passion, He lifts up His eyes to Heaven and prays to the Father. Then, before He ascends into Heaven, He csays He goes so that the Holy Spirit can come and “teach [mankind] all things,” something only an omnipotent God can do (Jn 14:26).
At the end of Matthew’s Gospel, Christ commissions His disciples to “make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit” (Mt 28:19). Baptism forgives sins, and only God can forgive sins, so it follows that we should be baptized in God’s name. Therefore, Christ reveals that the Father, the Son, and the Holy Spirit are God.
When speaking of the Trinity, we often use human concepts to explain the Persons’ relationship to one another. The beginning of the Gospel of John gives us insight into the processions (eternal derivations) of one member of the Trinity from another. These processions are eternal, meaning that the Son was never “born” as you and I are. Rather, the Father eternally begets the Son, meaning the Son has always and always will be “Sonning” (Thomistic Institute). John’s Gospel begins: “In the beginning was the Word, and the Word was with God, and the Word was God” (Jn 1:1). Jesus Christ, the Word existed in the beginning. He was with God (the Father) and He was God.
The Greek word used for “Word” in John 1 is Logos, which has many meanings, one of which is “Wisdom.” Thus, we can say that Wisdom has always been with the Father, and Wisdom is with or proceeds from the Father. We can think of the Holy Spirit as Love, and thus as proceeding from the Father and the Son. Love proceeds from Wisdom. These processions are eternal derivations, meaning that Christ never started to proceed from the Father, nor did the Holy Spirit ever start to proceed from the Father and the Son. Likewise, the Father never started to beget the Son. The relations between the Persons of the Trinity have always happened and will always happen, meaning that the Father continually begets the Son, the Son continually proceeds from the Father, and the Holy Spirit continually proceeds from the love between the Father and the Son.
The faithful have held the dogma of the Trinity since the beginning of the Church. However, there were many heresies in the succeeding centuries. These heresies primarily distorted the Divinity of Christ, either rejecting It entirely, or asserting that He was somehow less important than the Father or the Holy Spirit. Arguably the earliest heresy was Gnosticism. Gnosticism has reappeared throughout history, in various forms, often manifested by an “in group” who claims to have some secret knowledge, which others do not have. The early Church heresy of Gnosticism not only possessed this secretive, uncharitable aspect, but it also denied the Incarnation, because it thought the material world bad. Thus, anything, even human bodies, were evil. But if Christ never became man, He never truly died on the Cross, or suffered any of the physical torments of His Passion. If this is true, He has not saved us, for He did not shed His blood because He had no blood. Consequently, the denial of Christ’s Divinity is a manifestly false belief.
After the brunt of Gnosticism’s initial scourge came Arianism, proposed by Arius, an early church presbyter, which stated that the Son was not God, but a mediator between God and His creation. Arius largely based his position on Proverbs 8:22-31, a passage often attributed to the Second Person of the Blessed Trinity and/or the Blessed Virgin Mary. However, the passage does not imply that the Blessed Virgin Mary is God, and the Church does not teach as much. Rather, certain parts of the passage apply to the Son, and others to Mary. We often call the Son the Wisdom of God, yet there is also another type of wisdom which is created, as Proverbs 8:22 notes, personifying created wisdom: “The Lord created me at the beginning of his work” (Prbs 8:22). This created wisdom refers to the wisdom of creatures which God created in them when He created them. If someone is wise, he possesses created wisdom, by a participation in the Divine, Eternal Wisdom, Jesus Christ. Created wisdom is of course not God, for God is uncreated. Rather, this type of wisdom emanates from the Lord and enables believers to contemplate the Divine Majesty of God, by enabling one to grow in charity. He who is wise is charitable; and He who is charitable seeks always to gaze upon the principal object of His charity: the Lord.
If the Father, the Son, or the Holy Spirit was created, He would not be God. Father, Son, and Holy Spirit are coequal and coeternal, meaning that they are equal and have always existed and always will exist. If one of the Persons was created, He would be a creature, and so would not be equal to the other members of the Trinity.
Therefore, because God is Three in One, each member of the Trinity is 100% God. This is the central mystery of Christianity, and we will never comprehend it on this side of eternity. We believe it because God has revealed Himself to be Trinity. He did so throughout the scriptures, and, even before the scriptures were compiled (or even all of them written), Christians believed that God was Trinity. The Catholic Church did not fabricate this truth, for God reveals it in the Deposit of Faith that He has given to His Church.
Yet, God as Trinity may still confound us. Is this “Trinity” really existence itself? How can Divine Simplicity be so complicated? As God would not be God if we could understand Him, so God could not be Trinity if we fully understood what Trinity means. In fact, God seems so complicated to us because of His simplicity. A truth such as that of the Trinity is so far beyond our comprehension that simplicity seems to be the only logical answer to how God can be Trinity and yet completely simple. God has endowed us with extremely powerful intellects, and so we can even comprehend the seraphim, not by sight, but by comparing them with God. However, we cannot, even in our heart of hearts, comprehend God Himself, who “passes all understanding” (Phil 4:7). Pray about this truth and ask the Lord for guidance and read the Catechism and what the saints say on this subject, for their wisdom far surpasses anything said here.
We were not made for this world, or any of its creatures, but for God alone – to love Him for all eternity. Even in this world, when the lover gazes upon the beloved, he cannot comprehend his love for her entirely. There is some mystery, something that he knows is there, but cannot put a finger on. He does not so much possess his love, as the love with which He loves the beloved possesses him. “It is the nature of love to transform the lover into the object loved” (Opuscula, in duo praecenta). So God, Who possesses Himself in totality, draws up His creatures into the love with which He has loved them before He “formed [them] in the womb” (Jer 1:5).