ONE GOD OF THREE RELIGIONS?

Our Lord said the quote that you quoted, because he was fulfilling the prophecies of the Old Testament, He was referring to the commandments of the new law, the New church which He founded on Himself, based off of the Jewish religion. The Jews were called the chosen people only because they were the race of men by which God would allow humanity to attain heaven through the sacrifice of His Son. Prior to Our Lord, every holy person that died remained in what the Church calls Limbo, or the uppermost part of hell, where they did not suffer, but simply did not enjoy the vision of God. The laws of the old testament, the ones you are referring to, were only intended for the Jews up until the time of Christ and not after because they were the only covenant between God and man. They were the means by which the Jews proved their obedience to God's commands. Once Christ came, their obedience is proven through subjection and recognition of His Son, thus the emnity between the Jews and the Christians which has lasted since the founding of the Church. And the "until" of the old testament you referred to, as can be seen on numerous occasions in the old and new testament, doesn't mean "until" as we think of it, it basically means "never." Thus, the Catholic Church's doctrine on indefectibility (the Church will last until the end of time) which was always held since the time of St. Peter and the apostles who were the direct transmitters of Christ's teachings.

But we Muslims don't believe that Jesus is God. [Last time I said this some Christians go at me like a ton of ballast though]
===============Christians believe that Christ, as the Son of God, is God. Somewhat the same as your son is one with you, or would be if you had one.His existence is from the beginning and prophecy tells of his birth in Bethlehem. Christians believe that, you believe something different, which is your right.