James 2:19 (English-NIV)
You believe that there is one God. Good! Even the demons believe that--and shudder.

1 Corinthians 8:5-6 (English-NIV)
5 For even if there are so-called gods, whether in heaven or on earth (as indeed there are many "gods" and many "lords"),
6 yet for us there is but one God, the Father, from whom all things came and for whom we live; and there is but one Lord, Jesus Christ, through whom all things came and through whom we live.

John 17:3 (English-NIV)
Now this is eternal life: that they may know you, the only true God, and Jesus Christ, whom you have sent.

Ephesians 4:4-6 (English-NIV)
4 there is one body and one Spirit, just as you were called to one hope when you were called
5 one Lord, one faith, one baptism;
6 one God and Father of all, who is over all and through all and in all.

There is only one God and he is the Father. (Is God)
Jesus is the Son of God. (From God)
The Holy Spirit is the Spirit of God. (From God)

John 1:14 (English-NIV)
And the Word was made flesh, and dwelt among us, (and we beheld his glory, the glory as of the only begotten of the Father,) full of grace and truth.

Some people think this verse says that God became flesh.
Remember that God is too pure to look upon sin. So he sent his only begotten son into the world, so he could save the world.

Jesus is the Mediator between Man and God and the only name under heaven by which Man can be saved.

John 6:46 (English-NIV)
No one has seen the Father except the one who is from God; only he has seen the Father.
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John 1:18 (English-KJV)
No man hath seen God at any time, the only begotten Son, which is in the bosom of the Father, he hath declared him.

Only Jesus can show us God and only Jesus can bring us to God and only Jesus can redeem us back to God. God is our Father and he is one God and Jesus is the only born Son from God and the Word of God.

Please see my indepth study on this subject at http://www.heaven.net.nz/writings/trinity.htm