Thou wilt perform the truth to Jacob, [and] the mercy to Abraham, which thou hast sworn unto our fathers from the days of old.
Ver. 20. Thou wilt perform the truth to Jacob, and the mercy to Abraham] Heb. Thou wilt give; for all is of free gift. His love moved God to promise, his truth binds him to perform; 2 Samuel 7:18; 2 Samuel 7:21, "For thy word's sake, and according to thine own heart, hast thou done all these things." Having made himself a voluntary debtor to his people, he will come off fairly with them; and not be worse than his word, but better. Hence, Revelation 10:1, Christ is said to have a rainbow upon his head; to show that he is faithful and constant in his promises, and that tempests should blow over, the sky be cleared. "For this is as the waters of Noah unto me," saith the Lord: "for as I have sworn that the waters of Noah should no more go over the earth; so have I sworn that I would not be wroth with thee, nor rebuke thee. For the mountains shall depart," &c., Isaiah 54:9,10. God hath hitherto kept promise, with nights and days, Jeremiah 33:20; Jeremiah 33:25, that one shall succeed the other; therefore much more will he keep promise with his people.
Which thou hast sworn unto our fathers] And, in them, to us, by virtue of the covenant. So he spake with us, when he spake with Jacob at Bethel, Hosea 12:4; and that the promises sworn to the fathers of the Old Testament belong also to us of the New, see Luke 1:55; Luke 1:73,74. Now, that God swore at any time to them, or us, he did it for our sakes doubtless; "that by two immutable things, in which it was impossible for God to lie, we might have a strong consolation, who have fled for refuge to lay hold upon the hope set before us," Hebrews 6:17,18. See Trapp on " Heb 6:17 " See Trapp on " Heb 6:18 "
Gloria Deo in excelsis.