Learning from Christ, the apostles also taught the same thing about the true God:

“Yet there is for us only one God, the Father, who is the Creator of all things and for whom we live; and there is only one Lord, Jesus Christ, through whom all things were created and through whom we live.” (I Cor. 8:6 Good News Bible)

For the true Christians, the Father alone, and no other else, is the true God. The apostles never taught of a triune God. They never taught the Son and the Holy Spirit as other gods or persons of the so-called Trinity.

Not a new doctrine
That the Father alone is the true God is not a new teaching. This dates back to the early people of God. Moses said to the people of Israel:

“For I will proclaim the name of the LORD. Ascribe greatness to our God! … Do you thus requite the LORD, you foolish and senseless people? Is not he your father, who created you, who made you and established you?” (Deut. 32:3, 6 RSV)

The God of the Israelites is the Father whom they also recognized as the Creator. This belief has been held by them since ancient times (Isa. 64:4, 8 New International Version; Mal. 2:10 RSV).

The true God Himself recognizes no other God besides Him. And neither does He recognize any equal. He said: “I am God, and there is no other; I am God, and there is none like me” (Isa. 46:9 NIV). Who are we to insist then that aside from Him, there are still other gods who are like Him?

The Trinity is unscriptural
Although countless people in Christendom embrace the doctrine of the Trinity, those in the know readily admit that this is not found in the Bible. Joseph Pohle, a Catholic author in his book entitled, The Divine Trinity: A Dogmatic Treatise, wrote that, “It cannot therefore be seriously maintained that the mystery of the Divine Trinity was early revealed in the Old Testament” (p. 20). And neither can this doctrine be read in the New Testament as testified to by a catechetical book, The Teaching of Christ: A Catholic Catechism for Adults (p. 177). The writers of this book categorically state that, “The word ‘Trinity’ does not appear in the New Testament …”

The above testimonies are concurred to by Augustus Hopkins Strong, Doctor of Divinity, who says in his book, Systematic Theology, “the term ‘Trinity’ is not found in Scripture.” Strong also informs us that, “The invention of the term is ascribed to Tertullian.” (p. 69)

Thus, it should come as no surprise that the doctrine of the Trinity is not found in any part of the Bible. Believers of the Trinity, themselves, candidly admit that the doctrine is nowhere written in the Old and New Testaments. Such Trinitarian concept of God was only invented by Tertullian who lived sometime in the late second and early third century. Christ then had long ascended into heaven and His apostles had long been dead. Hence, they did not have anything to do with the evolution of such doctrine about God.