[Ali Imran]

In the begining there is the word and the word is God and dwells among us.
Who is the word?

Deuteronomy first.

I, and I alone, am God; no other god is real. I kill and I give life, I wound and I heal, and no one can oppose what I do.

Q: Who is the "I" there? 
A: The Father. 

Q: Why did the Father make it clear right from the very beginning that He alone is God? 
A: So that we know to reject satan who will want to mislead us by making us take some others as God.