Why Do Christians Think Jesus Is Their Messiah?

Ive study some judaism, islam, and other stuff and once was a Christian. But why do yall think Jesus is your Messiah? In accordance to belief, he was sent to ISRAEL. To fulfill Allah's promise of a Messiah and the annointed one. Us non Jews were not promised that, and our ancestors were not waiting on a Messiah. It is a promise to the Jews cuz they await another King David like figure. Those of us who arent Jew need it not since we never HAD a King David. As a former Christian, it all reads out like a bunch of disgruntled "goy" wanting to be apart of something.