Paul writes that Jews who reject Jesus are being preserved as a "remnant" by God's grace as an act of His divine mercy in order to fulfill the promises He made in the holy Jewish scriptures (Old Testament). God has allowed Jesus to be a "stumbling block" to the people of Israel so that their transgressions will allow the Gentiles to be "grafted in" to fully participate in the benefits of the covenant salvation promised to God's "chosen people"...His elect, who are the Jews. The hearts of the Israelites will remain hardened until "the full number of Gentiles comes in" and then *all* of Israel will be saved by God's endless mercy! Christians...rather than being the enemies of the Jews...instead draw nourishing "sap" from the covenant relationship established between God and the Israelite nation.