A) Purpose of all the messengers(prophets)sent from God was to guide people towards God, so they can live in peace with each other. So when Jesus came, he came for none but jews. He said this himself in his earthly life(He never said on his physical stay on earth that I came for non jews) He also said I came to revive the law(because law had been corrupted)Those who say OT is the basis of all Abrahamic faiths then refute the very purpose of coming of Jesus.(Same is acknowledged in Quran)Jesus came and left with his mission of correcting the law unaccomplished. OT was changed (read Jeremiah8:8)and New Testament or Gospel what Jesus himself taught from is not available today. The Mark, Mathew, Luke and John version of Bible were written 50 to 75 years after the ascension of Jesus. What Jesus himself said is written in Quran(what he did not, is not written in Quran because Quran was the book Prophet Muhammad came with and Prophet himself was role model for people to follow(like previous messengers were)Quran was from same one God therefore it has correct version of message from same one God, the sole creator of the universe. Now to follow up on the question those who raise this question should being intellectually investigative read Quran themselve and analyze its claims of being a divine book.
