In this and the following verse Paul applies the scripture passages to his present situation. Small number is translated by most as “remnant” (a synonym to the words used in 9.27: only a few).

God has chosen, because of his mercy (see New English Bible “selected by the grace of God”; An American Translation* “selected by God’s mercy”) is literally “according to the choice of grace.” The choice is God’s choice and the grace is God’s grace. In many contexts the nearest equivalent in English of the biblical concept of “grace” is mercy. The equivalent of because of his mercy may be “because he is so good to people” or “because he shows mercy so much.”

Quoted with permission from Newman, Barclay M. and Nida, Eugene A. A Handbook on Paul’s Letter to the Romans. (UBS Handbook Series). New York: UBS, 1973. For this and other handbooks for translators see here .