In the prior chapter, Abram saved his nephew Lot. Now God appears to Abram in a vision, and God unilaterally promises him that He will reward Abram greatly (1). This is a God Who loves to reward, all by His sovereign initiative. This sovereignly-given reward is what moves along the whole Bible - see the mediation on Matthew 6 on January 6, and see Hebrews 11:6.
But how will Abram be rewarded, since he has no heir (2)? God promises him that, despite his old age, he will have a son (4). And his offspring will number like the stars in the sky (5). And Abraham believes him. There are three angles to this moment that we must observe.
The first is God’s response to Abram’s faith - He credits his faith to Abram as righteousness. D.A. Carson explains this so well:
. . . The idea is that what God demands of his image-bearers, what he has always demanded, is righteousness—but in this sinful race what he accepts, crediting it as righteousness, is faith, faith that acknowledges our dependence upon God and takes God at his word. This faith of Abram is what makes him the “father” of those who believe (Rom. 4; Gal. 3).1
Now, despite Abram’s faith, God embarks on a physical act, which Abram needs to cement his faith (8). God, in v. 8-21, “cuts” a covenant with Abram.
This practice in ancient times was not unusual. A covenant was a solemn, public oath or promise that two people engaged in. To solemnize their oath, they would hold hands, and walk between the two pieces of the killed bull, essentially saying, “Thus be it down to either of us (what happened to the bull), if either of us break this covenant.”
What was unusual about this covenant was that it only involved one party. God, in the form of the flaming pot, is the only party Who walks between the pieces. God is unilaterally promising Abraham this great reward, and He is banking His entire reputation on fulfilling His gracious promise. This moment becomes the backbone of Abram’s assurance, and it is meant to assure all his offspring, who follow in his faith - see the last paragraph of Hebrews 6.
This assurance is crucial, for Abram will live to meet his son, but not the fulfillment of all these things. God, in His infinite wisdom, will wait to fulfill His promise until the sins of various people groups’ sins are “complete” (16). So Abram will still wander and wait. Our lives and God’s promises do not always follow the same timeline. Faith is hoping in what we cannot see, on the basis of what we can see - His very great and precious promises (2 Peter 1:4).
Carson, D.A. “For the Love of God” Vol. 1. January 14.