Remnant (λιμμα). Old word, but only here in N.T., but in papyri also and with this spelling rather than λειμμα. From λειπω, to leave.

According to the election of grace (κατ' εκλογην χαριτος). As in Romans 9:6-13. The election is all of God. Verse :Romans 11:6 explains it further.