After Abraham’s response of faith, which proved his genuine loyalty, God continues to speak to Abraham, saying “I am the Lord who brought you out from Ur of the Chaldeans to give you this land to possess” (15:7b). Having responded in faith, Abraham has accepted that this can be made to happen, even if his situation and circumstances seemed to militate against the possibility; but he does ask “O Sovereign Lord, by what can I know that I am to possess it?” (15:8) The Lord responded with directions concerning some animals, which would lead to a covenant ritual. As it relates to what Paul is attempting to prove in Romans four, given the opportunity to here enshrine circumcision as the proof of God’s covenant promise to Abraham, the proof comes in the form of yet one more thing for which Abraham will have to trust is going to come about under the ultimate control of this sovereign God.
Strangely, Abraham is told “Know for certain that your descendants will be strangers in a foreign country. They will be enslaved and oppressed for four hundred years. But I will execute judgment on the nation that they will serve. Afterward they will come out with many possessions. But as for you, you will go to your ancestors in peace a be buried at a good old age. In the fourth generation your descendants will return here” (15:13b-16b). The eighteenth verse stresses what it is that God is doing, as we read “That day the Lord made a covenant with Abram: ‘To your descendants I give this land” (15:18a). So here we have explicit language of covenant, and a specific promise related to Abraham’s descendants, with this following Abraham’s belief, which has induced the continued communication between God and Abraham, and there is still no circumcision (or any other visible or physical covenant marker besides loyalty). Though he does not offer any outward signs, can it be doubted that Abraham is operating under the auspices of God’s covenant with him? Of course not.
At least thirteen years later, as we press forward to chapter seventeen to hear God again speaking to Abraham, we hear Him say “I am the sovereign God. Walk before Me and be blameless. Then I will confirm My covenant between Me and you, and I will give you a multitude of descendants” (17:1b-2). We bear usefully in mind that it has been quite some time since Abraham has heard “a son who comes from your own body will be your heir” (15:4b). In the meantime, and according to his belief in God and his response of faith, Abraham has produced an heir, from his own body, with that heir being his son, Ishmael. In fact, those hearing the story would also have heard God speaking to Ishmael’s mother and saying to her (using language that is heavy with Abrahamic covenant implications ) “I will greatly multiply your descendants… so that they will be too numerous to count” (16:10).
This sounds quite similar to the words that have been spoken to Abraham in regards to his descendants. Assuredly, these words of promise, though offered to Hagar, would not go unheard by Abraham, and would be evidence, to him, of the faithfulness of his God. We simply cannot imagine Hagar keeping this experience from him. As one of Abraham’s wives, and as one who, as a servant in his household prior to gaining status as a wife, would have learned about the God that is said to have revealed Himself to Abraham, we can only imagine her excitedly sharing the good news with her husband, as it would have been received as yet another confirmation of the words of promise that had been previously directed only to Abraham himself. Hagar would not have heard them as an independent promise to her. She would have heard them in the context of the promise to Abraham, especially since she had been taken as his wife specifically in relation to Abraham’s belief in God that he would have countless descendants. For Abraham, Hagar and the son to be born through Hagar were integral components of the fulfillment of promise.
When Abraham hears God speaking again in the words that open the seventeenth chapter, and when those that hear the story of Abraham again here the voice of God, what is heard is renewed talk of a multitude of descendants that follows hard upon nearly identical words spoken to Hagar. Surely this of interest to someone like Paul, who has as his mission to throw wide the gate of entry into the fold of the covenant people of God, firmly believing that, in Christ, this covenant encompasses all peoples (and hence all creation as the land of promise), not being limited to the physical descendants of Abraham through Isaac or to those that take up covenant markers that the Abraham story clearly reveals to be of a secondary concern. To this point in the Abraham story, it has been well demonstrated that belief in God is the primary concern and the basis for a covenantal relationship.