The Catholics and the Protestants claim that they too believe that there is only one true God. However, they also uphold the doctrine that there are three persons in one God (they call it the doctrine of the Trinity). Thus, for them, there's God the Father, God the Son and God the Holy Spirit. If ask how these three persons become one God, the answer you are likely to received is that this is a mystery.
Which is truly biblical? The doctrine uphold by Catholics and Protestants that there are three persons in one God or the doctrine uphold by the Church of Christ that there is only one true God, the Father and no one else besides Him?
What the Old Testament
Teaches about God
Numerous passages of the Old Testament confirm the teaching that there is only one true God, the Father, and no one else besides Him. In Malachi 2:10, the Old Testament clear tells us that the one God who created us is the Father:
“Have we not all one Father? Did not one God create us? Why do we profane the covenant of our fathers by breaking faith with one another?” (Mal. 2:10 NIV)
Isaiah 64:8 confirms that the Father is the Lord who created us:
“But you are our father, LORD. We are like clay, and you are like the potter. You created us,” (Is. 64:8 TEV)
The Old Testament attests that there is no other God but the Lord (our Father):
“How great you are, O Sovereign LORD! There is no one like you, and there is no God but you, as we have heard with our own ears.” (II Samuel 9:22 NIV)
The Lord God Himself declares that there is no other God besides Him:
“Do not tremble, do not be afraid. Did I not proclaim this and foretell it long ago? You are my witnesses. Is there any God besides me? No, there is no other Rock; I know not one." (Is. 44:8 NIV)
The Old Testament further declares that there is no other god with Him:
“For I will give honour to the name of the Lord: let our God be named great. He is the Rock, complete is his work; for all his ways are righteousness: a God without evil who keeps faith, true and upright is he.
“So the Lord only was his guide, no other god was with him.” (Dt. 32:3-4 and 12 Bible Basic English)
Thus, the teaching of the Old Testament about God is clear, that there is one true God, the Father.
What the New Testament
Teaches about God
According to Apostle Paul, for true Christians there is only one true God, the Father:
“Yet for us there is but one God, the Father, from whom all things came and for whom we live…” (I Cor. 8:6 NIV)
They learned this from the Lord Jesus Christ who Himself taught that the Father is the only true God:
“After Jesus said this, he looked toward heaven and prayed: "Father, the time has come. Glorify your Son, that your Son may glorify you.
“Now this is eternal life: that they may know you, the only true God, and Jesus Christ, whom you have sent.” (John 17:1, 3 NIV)
According to Apostle Paul, the Father who is the one true God is the Father of the Lord Jesus Christ:
“If I have to ‘brag’ about myself, I'll brag about the humiliations that make me like Jesus. The eternal and blessed God and Father of our Master Jesus knows I'm not lying.” (II Cor. 11:30-31, The Message)
Even Apostle Peter attested that the one true God is the Father of the Lord Jesus Christ:
“Praise be to the God and Father of our Lord Jesus Christ! In his great mercy he has given us new birth into a living hope through the resurrection of Jesus Christ from the dead.” (I Peter 1:3 NIV)
Thus, the New Testament is also clear in its teachings about God, that there is only one true God, the Father.