God has not rejected His people whom He foreknew. Elijah pleaded with God against Israel when they killed His prophets, tore down His altars and tried killing him. God said He reserved a remnant of 7,000 chosen by grace who did not worship Baal. Grace supersedes works. Those chosen among Israel obtained what they sought but the rest were hardened. As it was written, God gave them a spirit of stupor so their eyes could not see and their ears could not hear. David said their table became a snare, trap and stumbling block (Rom. 11:1-10). God chose a remnant among Israel according to grace so they could worship Him.
Because of their transgression, salvation came to the Gentiles to make Israel jealous. Paul as an apostle to the Gentiles hoped to arouse Israel to envy and save some of them. Their rejection is riches and reconciliation of the world. Israel's acceptance is life from the dead since the root and branches are holy. Some of the branches were broken off because of unbelief so Gentiles could be grafted in as the wild olive shoot and share in the nourishing sap from the olive root. Do not be boastful but continue in his kindness through faith to prevent being cut off. If God grafted branches into a cultivated olive tree, how much more will natural branches (Israel) be grafted into their own olive tree through faith (Rom. 11:11-24). God saved Gentiles by grace through faith using sin and disobedience to reconcile the world.
Israel experienced a partial hardening until the full number of Gentiles came in. All Israel will eventually be saved when the Deliverer comes from Zion to remove ungodliness from Jacob and establishes His covenant to take away their sins. They were enemies concerning the gospel, but election allowed God to love them through the patriarchs. God's gifts and His call are irrevocable. Gentiles who were disobedient received mercy as a result of Israel's disobedience. God bound all men over to darkness so He might show mercy to all (Rom. 11:25-32). God called Israel and Gentiles to salvation by taking away their sins.
Oh, the depths of the riches of the wisdom and knowledge of God. How unsearchable are His judgments and unfathomable His ways. No one knows God's mind or be His counselor. You cannot give to God and be paid back. God originated all things for His glory (Rom. 11:33-36). God originated all things to show His glory beyond comprehension.
The most appropriate response to God's mercy is offering your body as a living and holy sacrifice for a spiritual service of worship. Do not be conformed to this world, but be transformed by the renewing of your mind to prove the good, acceptable and perfect will of God (Rom. 12:1-2). Offer your body as a living sacrifice without compromise by renewing your mind to prove God's perfect will.
Think realistically without boasting according to the faith God gives you. Each member of Christ's one body belong to each other with different functions. We have different spiritual gifts according to the grace given us like prophesying according to the proportion of his faith, serving, teaching, encouraging, giving generously to the needs of others, leadership that governs diligently and showing mercy cheerfully (Rom. 12:3-8). Discover and exercise your spiritual gifts by thinking clearly according to the faith God gives you.
Offer sincere love by hating evil and clinging to good. Be devoted in brotherly love by honoring others above yourself. Serve the Lord zealously with spiritual fervor. Rejoice in hope, patient in tribulation, devoted to prayer, contribute to the needs of the saints and practice hospitality. Bless and do not curse those who persecute you. Rejoice with those who rejoice and weep with those who weep. Live in harmony with one another by associating with the lowly without conceit. Do not repay evil for evil but do what is right. Work hard being at peace with all men. Let God take vengeance since He will repay injustice. If your enemy is hungry, feed him, if he is thirsty, give him a drink for you are heaping coals upon his head. Do not be overcome by evil, but overcome evil with good (Rom. 12:9-21). Serve others by honoring and meeting real needs.
Meditate and revel in the truths of God's grace producing the following: worshiping Him, reconciling the world, removing sin, showing His glory, offering your body as a living and holy sacrifice, exercising spiritual gifts and serving others by honoring and meeting real needs.