Luke 1:72

To show mercy towards our fathers, And to remember his holy covenant; The oath which he sware to Abraham our father.

These words show the connection between the old and the new covenants. The covenant with Abraham had envisioned the blessing of "all the families of the earth" through the glorious Seed (singular) which is Christ (Genesis 12:1-3). Moreover, God had confirmed the covenant promise to Abraham with an oath (Genesis 22:16; Hebrews 6:13-15). Just as God's promise to Abraham of a son was delayed of fulfillment until it seemed no longer possible, so also the establishment of Messiah's kingdom had been held in abeyance for centuries, the last voice of prophecy having expired with Malachi; but wow all was to be fulfilled. As to who were, and who were not, true sons of Abraham and thus entitled to the promise, there was widespread misunderstanding. The materialistic, secular priests, and a majority of the people, thought that mere fleshly descent from Abraham was all that mattered; but, of course, it was only to the "spiritual seed," the people of like faith and character with Abraham, that the promise really pertained. It was the great mission of John the Baptist to enlighten Israel on this very point.