The groups that oppose the dogma of the Trinity will often point to the many Scriptural passages that tell us that God is “one.” Passages from the Old Testament that speak to this include Deuteronomy 6:4 “Hear, O Israel: The Lord our God is one Lord,” and Isaiah 45:5 “I am the Lord, and there is no other; besides me there is no god,” and Deuteronomy 1:30 “The Lord your God, who goes before you, is the one who will fight for you” (NSRVCE). God also consistently speaks in Scripture with the language “I am.”
There are also New Testament passages that tell us that God is “one” such as:
John 17:3 “And this is eternal life, that they know thee the only true God, and Jesus Christ whom thou hast sent”
Galatians 3:20 “Now an intermediary implies more than one; but God is one”
1 Corinthians 8:4 “there is no God but one”
Mark 12:29 “The first is, Hear, O Israel: the Lord our God, the Lord is one.”
For those of who profess a belief in the Trinity these passages are not difficult to resolve as we absolutely agree that there is one God. That is a basic principle of the Trinity.
But we also see in Scripture some interesting language where God refers to Himself as plural. In creating man for example, Scripture says “Then God said, “Let us make man in our image, after our likeness” (Genesis 1:26). When Adam and Eve sin, God says that “Behold, the man has become like one of us, knowing good and evil” (Genesis 3:22).
Non-Trinitarians may view these verses as God referring to Himself and the angels. This seems to me to be a bit problematic for it credits the angels as creating along with God.
We also see passages in Scripture that equate the reference to “us” as being the one Lord. In Genesis 11:7-8 during the tower of Babel story, God says “’Come, let us go down, and there confuse their language, that they may not understand one another’s speech.’ So the Lord scattered them abroad from there over the face of all the earth, and they left off building the city.” And in Isaiah 6:8 we read “And I heard the voice of the Lord saying, ‘Whom shall I send, and who will go for us?’”
St. Augustine taught us that the “New Testament lies hidden in the Old and the Old Testament is unveiled in the New.” We see the mysterious “us” come to light in the New Testament at the Baptism of Christ when the three persons are revealed together for the first time:
Matthew 3:16-17 “And when Jesus was baptized, he went up immediately from the water, and behold, the heavens were opened and he saw the Spirit of God descending like a dove, and alighting on him; and lo, a voice from heaven, saying, ‘This is my beloved Son, with whom I am well pleased.’”
And when Jesus gives the apostles the great commission, he explicitly tells them “Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit” (Matthew 28:19). It is very interesting to note here that in the formula for baptism Jesus names the three distinct persons of the Trinity, but tell us to baptize in the “name” of them, not “names.” One God, three persons.
More to come on the Scriptural evidence for the Trinity.