The God of Abraham, Issac and Moses, is the one and only God. Where the trouble starts is in each religions belief of where the "underlings" to God come into the picture and who and what they represent. For Christians, Jesus Christ is the Son of God, the last part of the Most Holy Trinity, the Son of Man, and a half dozen other titles of equal grandeur and import.
The Jews and Muslims see Jesus as nothing more than a prophet, honored and important surly, but not God Himself. The old Testament speaks to the Jewish outlook on God, the Koran the outlook on God, and Holy Scriptures or the New Testament on how the Christians view God. Many, many problems arise in the fine details of this part of religion.
Jesus Christ did not start the Christian Church. He had no such intention. St. Paul was the first Christian and started what became a general mess. If Christ came back today and saw what was built in his name, he would puke! You think he lost his cool with the money changers in the Temple? I would not wanna be near Him when he saw the million dollar edifices built to God and in His name. His message was simple: love each other. Love God. From that, we have Christian scriptures which didn't begin until the year 90 A.D., when the only possible person still alive when Christ walked the earth, might have been St. John. John was the only Apostle to die of natural causes. He was the only one to live into his 90's, and it is highly doubtful that he had anything to do with the Gospel named after him.
So, the Holy Scriptures, which were written by man but inspired by God, certainly did not record anything directly from anyone who was alive when Jesus was alive. This in itself, should give pause to many. So none of the Gospels can claim that this person or that person heard Jesus say this... The fact that most of the Old Testament, if not all of it is made up of fables, brings us to a greater loss of common sense. The fundamentalists love to quote the O.T. like it was handed down by God. It was not! If it were, that would make God a vengeful, hating God, who would entice mankind to do all sorts of things in his name. More thoughts later.