The Holy Trinity is revealed both in the Old Testament and in the New Testament. In the Old Testament, the Trinity is revealed in subtle ways; in the New Testament, the Trinity is revealed fully and plainly, beginning at the Baptism of our Lord.
The Holy Trinity is one God in three Persons, Father, Son and Holy Spirit. These Persons are distinct, but not separate, and are not three gods. They are One God because They are one in essence or nature. The Father is the unbegotten Fountainhead of Deity. The Son is eternally begotten of the Father (Jn 1:18; 3:16; 16:28). The Holy Spirit is the Helper (Jn 14:16) and Spirit of Truth (Jn 14:17; 16:13), Who proceeds from the Father (Jn 15:26).
The Holy Trinity Created the World
Genesis 1:1 – God the Father created the heavens and the earth. The Creed says: “I believe in one God, the Father Almighty, Maker of heaven and earth.”
Genesis 1:2 – The Spirit of God is the Holy Spirit. He hovered over creation in creative power and equality with the Father. He co-created with the Father.
Genesis 1:3 – As the Word of God, the Son made the light (Jn 1:1-3). With creative power and equality with the Father, He also co-created with the Father and the Spirit.
Genesis 1:26 – The pronouns “Us” and “Our” reveal a plurality of divine Persons. These Persons are the Father, Son, and Holy Spirit operating in complete unity out of the one divine Nature.
The Holy Trinity Saves the World
Isaiah 63:16 – The Father is our Redeemer. He not only created the world but redeems it as well.
Psalm 2:7,8 – The Father’s decree reveals the Son as inheriting the world. This inheritance is the people saved by the Son.
Isaiah 6:1-3 – The words “Holy, Holy, Holy” declare the three Persons who save us. The name “Lord” declares the one essence of the Three.
Isaiah 44:3 – The Father pours out His Spirit on people like water on dry ground. The Holy Spirit quenches the thirst of the person who thirsts for salvation.
Isaiah 48:16, 17 – The Son declares that the Father and the Spirit sent Him to redeem the world. Although the Son alone became a Man, all three Persons save mankind.
The New Testament Affirms the Holy Trinity in the Old Testament
John 1:1-3 – The Word is the Son of God, who was present with the Father at the beginning of creation. He was Co-worker with the Father in creating the world.
John 8:58 – Jesus identifies Himself as having existed before Abraham. Before His coming in the flesh as Man, Jesus existed as the eternal Son of the Father, for He is begotten from the Father before all time and ages. He appeared to Moses in the burning bush and proclaimed Himself as “I Am” (Ex 3).
Acts 2:17 – The Holy Spirit’s descent at Pentecost affirms His presence in the Old Testament (Joel 2:28-32).
Hebrews 1:8-10 – This Scripture affirms the Father is speaking to the Son in Psalms 44:7 and 101:26-28, in which the Father acknowledges the Son as God and Creator of the world. For the Son was the Father’s Co-worker in creation.
The Incarnate Son Fully Reveals the Holy Trinity
Luke 1:35 – At the Annunciation, the Holy Spirit, the “power” of God the Father (“the Highest”), overshadowed the Virgin Mary; and she gave birth to the Son of God in His flesh.
Matthew 3:16-17 – When the Son of God was baptized in the Jordan by John, the Father’s voice was heard from heaven, and the Holy Spirit descended on Him like a dove. As the main hymn for the Feast of the Theophany says, “When You, O Lord, were baptized in the Jordan, the worship of the Trinity was made manifest.”
Source: The Orthodox Study Bible, St. Athanasius Academy of Orthodox Theology, 2008.