It was God’s purpose to include, from all eternity, the entire world in His mercy toward Israel. At the very beginning, when God told Abraham, “I will…curse him that curseth thee,” He also declared, “In thee shall all families of the earth be blessed” (Genesis:12:3). That amazing guarantee was repeated again to Abraham (Ibid., 22:18), later to his son Isaac (Ibid., 26:4), then to Jacob (Ibid., 28:14). This promise, of course, could be fulfilled only through the Messiah, descended from Abraham, Isaac, and Jacob. He would come to pay the full penalty for the sins of all mankind. “All families of the earth” could be forgiven and brought into unbroken fellowship with their Creator – if they were willing to accept salvation on His terms.
The Messiah would not suddenly appear on earth out of thin air. Nor would He step out of a UFO and declare, “Voilà! Here I am, the long-awaited Messiah!” He required a genealogy of human ancestors in order to be a genuine man.
He had to be God in order to be without sin and capable of paying the infinite penalty His own justice demanded for the sins of mankind. Yet He had to be a genuine flesh-and-blood man in order to pay the penalty on behalf of all mankind. God chose Abraham, and through him, Isaac, Jacob, and King David (and revealing His grace and forgiveness, even the harlot Rahab and Ruth the Moabitess), to be the ancestors of the Messiah. The Messiah had to be, and is, a Jew – another reason why God has a special place in His heart for Israel.