Kings Saul and David, the first two kings of Israel are symbolic of Judaism and Christianity. Like Judaism, Saul came first, chosen by God. Like Judaism, Saul was rejected by God. And just as the new covenant in Jesus Christ replaced the old covenant, so God chose David to replace Saul. And just as God gave better promises to David than he gave to Saul, we have better promises in Jesus Christ than were given by Moses. And as God promised David that his throne would endure forever, that he would never reject David or his descendants as he rejected Saul, so the new covenant in Jesus Christ, the son of David, will last forever and never be replaced.
David committed sins. He was murderer and an adulterer. He was a liar too. Though Saul was rejected for disobedience, for failing to follow the letter of the command, David certainly did enough bad things of his own, worse even. So too Christians have often failed, and every Christian does fail, to live a holy life. In rejecting Saul, God was not rejecting the man so much as he was rejecting the dynasty. In rejecting Judaism, God is not rejecting the people but the idea that anyone could keep the law and be righteous through works of the law and animal sacrifices.
So in relations between the Church and Jews, we Christians should take our cue from how David respected Saul. Even when Saul was trying to kill David, David would not harm Saul, since he dared not touch the Lord’s Anointed. Once chosen by God, the man was forever holy. We do not dare harm the Jewish people, for they are the chosen people, and though God rejects the old covenant, he is faithful to the end.
Why does God make a covenant and then reject it? At the time that God chose Saul, he knew that he would reject him later for failing to obey. At the time that God gave a covenant to Jacob and his offspring, he knew that he would reject them later for failing to keep the covenant. But Saul built up the kingdom that would become David’s kingdom. He prepared the way. And the Israelites built up the religious sensibility that would belong to all the first Christians. They prepared the way.