In John 1:1-2
In the beginning was the Word, and the Word was with God, and the Word was God. He was with God in the beginning.
This shows us that Jesus was the Word, and the Word was with God, just as the three in one: God, Jesus, Holy Spirit. Although they are three separate beings, they are still one person.
Relating to an example that we can better understand by todays thoughts: I am a woman- a mother, a sister, and a daughter...I am three people, yet still one person. 

Very good verse. Is this also an answer for the question posted by jlim on [John 1:1]?