First, the apostle wanted to assert that God’s decree in election is absolute and irrevocable. Whatever happens in human history, in everything God works his sovereign will, and that will is to save all his elect (whether Jew or Gentile) through Jesus Christ. Nothing will ever thwart God in this sovereign decree.
Secondly, although the Jews had been given the gospel first, and many had refused it, and, consequently, God had taken it to the Gentiles, the apostle was determined to stop Gentile believers vaunting themselves over Jews.
Thirdly, the apostle was in anguish that so many of his fellow-Jews were rejecting Christ and his gospel, and he wrote to try to provoke them to call upon the name of Christ and be saved. As he told the Corinthians (1 Cor. 9:19-23), he would do what he could to secure the salvation of sinners – especially, in Romans 11, his fellow-Jews. Do not miss his limited aim in this: ‘I have become all things to all men so that by all possible means I might save some’ (1 Cor. 9:22); ‘some’ not a huge number.
The apostle’s overall purpose in writing Romans 11 (indeed, Romans 9 – 11) was, of course, the glory of God: ‘Oh, the depth of the riches of the wisdom and knowledge of God! How unsearchable his judgements, and his paths beyond tracing out!... For from him and through him and to him are all things. To him be the glory forever! Amen’ (Rom. 11:33-36).
Gay puts forward his exegesis of Romans 11 because it is consistent with the apostle’s stated aims, does not hark back to the old covenant, but seeks to point to Christ and to draw sinners to trust him as Lord and Saviour – and all for the glory of God
ROMANS 11 - David H.J. Gay 2015-09-16