This chapter takes up the question of Israel's future, and in respect to the condition of Israel, who have transgressed and are guilty before God, but who can appeal to Him because of the unconditional promises made to Abraham. Nothing can change God's purposes and promises.
But they "are not all Israel which are of Israel." They have rejected Christ in whom are all of the promises. They have lost their rights to these promises; yet the purpose of God in regard to election shall stand entirely upon grace.
The apostle grieved for his kinsmen according to the flesh. The children of promise are the only ones who have a right to be called the seed of Abraham.
"I will have mercy on whom I will have mercy." It is God who shows mercy. This is His divine right.
God can also show His power. Pharaoh was an example of this. His heart was not hardened until he first refused God's servants and their message, then God hardened his heart. The Potter has power over the clay.
God endured the vessels of wrath, fitted for destruction by their own rejection of God and His claims, in order that He might make known the riches of His glory and grace on the vessels of mercy, the Jews and Gentiles.
The Gentiles attained unto righteousness by faith, but Israel under the law has not. "They sought it not by faith, but... stumbled at that stumbling stone," that "rock of offense," Christ!