isaiah 63:16 Doubtless thou art our father, though Abraham be ignorant of us, and Israel acknowledge us not: thou, O LORD, art our father, our redeemer; thy name is from everlasting. - Free Bible Online

      16. thou . . . father--of Israel, by right not merely of creation, but also of electing adoption (Isa 64:8; De 32:6; 1Ch 29:10).
      though Abraham . . . Israel--It had been the besetting temptation of the Jews to rest on the mere privilege of their descent from faithful Abraham and Jacob (Mt 3:9; Joh 8:39; 4:12); now at last they renounce this, to trust in God alone as their Father, notwithstanding all appearances to the contrary. Even though Abraham, our earthly father, on whom we have prided ourselves, disown us, Thou wilt not (Isa 49:15; Ps 27:10). Isaac is not mentioned, because not all his posterity was admitted to the covenant, whereas all Jacob's was; Abraham is specified because he was the first father of the Jewish race.
      everlasting--an argument why He should help them, namely, because of His everlasting immutability.

JFB.