Romans 11:15

For if the casting away of them is the reconciling of the world, what shall the receiving of them be, but life from the dead? "casting away of them" -"them" here refers to the unbelieving segment of the Jewish race, for God never did "cast away" "his people" (i.e. the section that manifested faith in Him and His Son) (Romans 9:1). God only 'cast's away' unbelievers (Romans 11:20)

"reconciling of the world" -obviously, not every inhabitant in the world. Jewish rejection, enabled the non-Jewish world to hear the message of reconciliation. (Compare Romans 11:11, Romans 11:11 'salvation has come to the Gentiles')

"what shall the receiving of them be" -'what will their acceptance and admission mean?' (Amp)

"receiving" -4356. proslepsis pros'-lape-sis; from 4355; admission: -receiving. To take to oneself (Robertson p. 395)

On what basis will unbelieving Jews be 'accepted' by God? Clearly, if they abandon their unbelief and turn to faith towards God! (Romans 1:16; Romans 11:23) And what will happen if 'some' do this? They will have spiritual life!

'The casting away of (unbelieving) Jews did not bring about the reconciling of the whole world (every Gentile), nor does "the receiving of them" mean that all Jews would be restored to God's favor...Hence, receiving. Jew back into favor with God is as life from the dead. The conversion of ANY SINNER to Christ is life from the dead.' (Romans 6:13 'as those alive from the dead') Note: The Prodigal Son is an illustration of lost 'Jews', who had once again found life! (Luke 15:24; Luke 15:1)

'Even in their cast away state, the unbelieving Jew is no farther from salvation than the once alienated Gentile was. Grace will still bless the believer. God has sworn to bless the believer and he will not turn from such. promise!' (McGuiggan p. 326)