The reason I said the Christian god has a multi-personality problem is because Christianity claims to be following the monotheistic God of Israel, yet, they will say 'He is a compound god of sorts, being "the Father, the Son and the Spirit."' With this backdrop of Jesus being "God", he is praying to his own self - the monotheistic God - but to the greater part of this tri "Godhead" - to the Father. If this is not clear, then let me put it in another way: Christianity claims that Jesus is a part of the monotheistic God of Judaism (whom they define as a tri-natured Godhead.) Therefore, when Jesus prays, he is praying to himself basically. We see this is the famous prayer called "the Lord's prayer" where Jesus says "our Father Who art in heaven..." and many other places in the gospels.
The definition regarding "who" the Christian god is all depends on what sect or denomination you bump into. For there are at least 5 different forms of the Trinity or some "Tri" type of doctrine affiliated with that god. Others, however, will see three different gods, deities or heavenly realm people/individuals. Furthermore, there are some other sects of Christianity that deem that there are only two individuals [i.e., the Father and the son [Jesus] while the "spirit" is some type of force.]
All of these beliefs go against Judaism. Judaism's God is purely a monotheistic God. The messiah to come must be the God of Israel's greatest servant, even far greater than Moses himself.
The moshiach/messiah/christ of Judaism is not divine, nor eternal, but a made being like everyone else.
Why does Christianity think Jesus is God? Well, its because of what their "New Testament" manuscripts say!! Here are some examples...
In the "Gospel of John" this is what it says in
"In the beginning was the Word, and the Word was with God, and the Word was God... All things were made by him [the Word]; and without him was not any thing made that was made... And the Word was made flesh, and dwelt among us."
In Chapter 8 we see Jesus talking to his own disciples, yet "prunning" them to see if they can handle more of the supposed "truth" concerning himself... let's read...
Your father Abraham rejoiced to see my day: and he saw [it], and was glad. Then said the Jews unto him, Thou art not yet fifty years old, and hast thou seen Abraham? Jesus said unto them, Verily, verily, I say unto you, Before Abraham was, I AM [John 8:56-58].
The term "I Am" is suppose to be a throw back to Exodus 3:14 where the God of Israel is talking with Moses. Here is that verse from the holy Torah...
"And God said unto Moses, I AM THAT I AM: and he said, Thus shalt thou say unto the children of Israel, I AM hath sent me unto you."
And after eight days again his disciples were within, and Thomas with them: [then] came Jesus, the doors being shut, and stood in the midst, and said, Peace [be] unto you. Then saith he to Thomas, Reach hither thy finger, and behold my hands; and reach hither thy hand, and thrust [it] into my side: and be not faithless, but believing. And Thomas answered and said unto him, My Lord and my God.