The Bible clearly teached that God created the heavens and the earth, that there is only one true God for worship and that God is one.
Deu 6:4 Hear, O Israel: The LORD our God [is] one LORD
Gal 3:20 Now a mediator is not [a mediator] of one, but God is
1Cr 8:6 But to us [there is but] one God, the Father, of whom [are] all things, and we in him; and one Lord Jesus Christ, by whom [are] all things, and we by him.
Eph 4:6 One God and Father of all, who [is] above all, and through all, and in you all.
1Ti 2:5 For [there is] one God, and one mediator between God and men, the man Christ Jesus;
The Bible also tells us what God is...and in not:
Jhn 4:24 God [is] a Spirit: and they that worship him must worship [him] in spirit and in truth.
Col 1:15 Who is the image of the invisible God
Num 23:19 God [is] not a man, that he should lie; neither the son of man, that he should repent
Jam 1:13 Let no man say when he is tempted, I am tempted of God: for God cannot be tempted with evil, neither tempteth he any man:
God is spirit and invisible. God is not a man, nor the son of Man and cannot be tempted.
God has no beginning or end. Jesus had a 'genesis' (beginning) at his birth although God knew about him in his (God's) foreknowledge.
Jesus was visible, a man, frequently referred to as the son of man, and was tempted in all ways as we are.
God is the father of Jesus Christ.
Jesus Christ is the only begotten Son of God.
Jesus had a separate will from his Father.
Jesus is subordinate to God.
Jesus is God's representative to man.
Jesus is the mediator between man and God.
Jesus died for our sins.
God raised Jesus from the dead.
God caused Jesus to ascend to a place at his (God's) right hand.
There is but one way to God and that is through Jesus Christ.
If one confesses Jesus as Lord and believes in his heart that God raised him from the dead, one will be saved.
But what we don't see in the Bible are "Trinity", "God the Son", "Jesus is God", "True God and True Man", "Three in One", "Triune God" or any of the other phrases used to describe this doctrine.
So when I say that I believe that Jesus Christ is the Only Begotten Son of God who lived a perfectly sinless life, died for our sins, was raised on the third day, currently sits at that right hand of God and will one day return for his saints, where is the flaw?
But I can and have shown mulitple flaws in the reasoning of three being really one; frequent contradictions to the Bible with the notion of Jesus being God and Flesh; and just plain loss of common sense! If Jesus is God then who did he pray to? Who did God call his beloved son? If Jesus is God, then no one saw him because God is invisible...