“Above all guard for me this great deposit of faith for which I live and fight, which I want to take with me as a companion, and which makes me bear all evils and despise all pleasures: I mean the profession of faith in the Father and the Son and the Holy Spirit. I entrust it to you today.” These are the words that St. Gregory of Nazianzus chose to impress upon the catechumens of Constantinople the importance of the mystery of our Trinitarian God. This belief in one God who is three divine Persons has been entrusted to the Church: it is Her job to protect and defend it so that it can be passed down to Her children throughout the ages. This belief is our heritage; it is our great privilege and grace to be taught from an early stage in our faith journey about the nature of the God who created us. Holy men and women in our history have died rather than give up their duty to guard this dogma—it is through their holiness and courage that God’s grace has operated so that we now still have and believe this fundamental doctrine. 

Of course, our belief that God is a Trinity—one God in three divine Persons—is a great mystery of our Faith. This is not the sort of mystery that fills detective novels: it is not a mystery that can be solved. Instead, this mystery of our Faith is a mystery in the sense that it can never be fully understood. As we grow in sanctity, we may come to understand more and more deeply, but we will never be able to fully understand how God can be one and yet three until we are with Him in heaven. 

The doctrine of the Holy Trinity is Scriptural and can be found in many places in the Bible. Starting in the Old Testament, one way in which the Trinity is revealed is the clear indication of plurality in God when three men appear to Abraham to prophesy that Sarah will have a son: “The Lord appeared to Abraham near the great trees of Mamre while he was sitting at the entrance to his tent in the heat of the day. Abraham looked up and saw three men standing nearby” (Gen 18:1-15). First Scripture tells us clearly that this is the Lord appearing to Abraham, who sees, importantly, three men standing in front of him. Another instance is in Isaiah 6:3: “Holy, holy, holy is the Lord of hosts!” This three-fold “holy” is a Trinitarian formulae known as the “Trisagion.” In the New Testament, the Trinitarian formulae can be seen in many places. Notably, in the Baptism of Jesus, we hear the Father blessing the Son and a dove appearing, indicating the Holy Spirit: “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” (Matthew 3:16-17). Secondly, in the Great Commission Jesus says to baptize people in the “name of the Father, Son, and Holy Spirit” (MT 28:19). It is clear from Scripture that God intends us to understand Him as being three Persons. 

Additionally, throughout the Bible, there are many verses that confirm the divinity of each Person of the Holy Trinity. The divinity of the Father is referenced in many places in Scripture, perhaps most memorably in Matthew 6:9-13 as Jesus teaches his followers to pray to God the Father in the Our Father. In the beauty of the beginning of the Gospel of John, it is apparent that both God the Father and God the Son are divine, since both have existed eternally and it is from the Father that the Son comes: “In the beginning was the Word, and the Word was with God, and the Word was God. He was in the beginning with God. All things came into being through him, and without him not one thing came into being” (John 1:1-3). In the Gospel of Matthew, Christ is worshipped as God: “And they came to him, took hold of his feet, and worshiped him” (Mt 28:9). In regards to the divinity of the Holy Spirit, there is John 14:16, Jesus promising to send the Advocate, and 1 Cor 6:19, where Paul discusses the human body as the temple of the Holy Spirit. Lest this emphasis on the divinity of the three Persons lead anyone to think there are three gods, God gives us the great commandment, commanding all to acknowledge that there is only one God (Deut 6:4-5 and Mark 12:29). 

Throughout the Church’s history, this belief in the Holy Trinity has been defined, confirmed, and protected, time after time—particularly in early Church councils. At the council of Nicea, it was stated that Jesus is truly God the Son. Both the Father and Son have the same nature, the same substance and Jesus, God the Son, proceeds by true generation. Additionally, it was defined that Trinity is the one God, in different Persons. At the first Council of Constantinople, the equal divinity of Trinity (that the Father, Son, and Holy Spirit are all equally God) was clearly defined. 

As we approach Trinity Sunday, let us take St. Gregory’s words to heart and guard this belief that has been entrusted to us, letting it be our companion that protects and guides us through our lives. Blessed Trinity, Father, Son, and Holy Spirit, have mercy on us!