And if [they were selected] by God’s unearned favor, [then] the choice is not based on the good that people may do. Otherwise, God’s favor would not be [really] unearned.
Why? Because they did not [attempt to do it] by faith [in Him], but by trying to fulfill all the requirements [of the law]. So, they stumbled over “the stumbling stone,” [i.e., the Jews refused to become obedient to Christ. See I Pet. 2:6-8].