Today we hear how God comes to Abraham in a dream, tells him not to fear, and promises him a son. This passage is in many respects reminiscent of the Annunciation of the Holy Theotokos that we celebrated on Saturday. Both Abraham and the Virgin Mary are told not to fear and are promised a seemingly impossible thing that rather startles them. And this parallel is not accidental, for Isaac, the son who is promised to Abraham, is seen by the Fathers as prefiguring Jesus Christ. As Saint Ambrose of Milan writes,
… he is speaking of holy Isaac. For this reason he added ‘who will come out from you.’ In fact, the one who truly came out of Abraham is the one who was born of a legitimate marriage. But in Isaac, the legitimate son, we can see the One who is the true legitimate son, the Lord Jesus, of whom at the beginning of the Gospel according to Matthew we read that he is the son of Abraham. He was the true heir of Abraham, bringing renown to the descendants of the progenitor. Through him Abraham looked up to heaven and understood that the splendor of his posterity would be no less luminous than the radiance of the stars of heaven.
Thus, while God does promise to fulfill Abraham’s immediate needs, there is also a longer-term and more transcendent promise involved. Saint Ambrose continues,
The holy and prophetic mind is more concerned with an eternal posterity. What Abraham desires is in fact the offspring of wisdom and the inheritance of faith. This is why he says, ‘What will you give me, since I am about to depart without children?’ What he desired was the progeny of the Church. What he was requesting was a descendancy that would be not servile but free, not according to the flesh but according to grace.
A Reading from the Book of Genesis 15:1-15:
After these things the word of the LORD came to Abram in a vision, “Fear not, Abram, I am your shield; your reward shall be very great.” But Abram said, “O Lord GOD, what wilt thou give me, for I continue childless, and the heir of my house is Eliezer of Damascus?” And Abram said, “Behold, thou hast given me no offspring; and a slave born in my house will be my heir.” And behold, the word of the LORD came to him, “This man shall not be your heir; your own son shall be your heir.” And he brought him outside and said, “Look toward heaven, and number the stars, if you are able to number them.” Then he said to him, “So shall your descendants be.” And he believed the LORD; and he reckoned it to him as righteousness.
And he said to him, “I am the LORD who brought you from Ur of the Chaldeans, to give you this land to possess.” But he said, “O Lord GOD, how am I to know that I shall possess it?” He said to him, “Bring me a heifer three years old, a she-goat three years old, a ram three years old, a turtledove, and a young pigeon.” And he brought him all these, cut them in two, and laid each half over against the other; but he did not cut the birds in two. And when birds of prey came down upon the carcasses, Abram drove them away.
As the sun was going down, a deep sleep fell on Abram; and lo, a dread and great darkness fell upon him. Then the LORD said to Abram, “Know of a surety that your descendants will be sojourners in a land that is not theirs, and will be slaves there, and they will be oppressed for four hundred years; but I will bring judgment on the nation which they serve, and afterward they shall come out with great possessions. As for yourself, you shall go to your fathers in peace; you shall be buried in a good old age.