GOD'S TIME SCALE is so different from ours. Abram wants a son, and feels his time is running out; God envisages a race with countless millions of descendants. Abram feels his life is approaching its termination with nothing very much settled as to God's purpose in calling him out of Ur of the Chaldeans; God sees the entire course of redemptive history.
What God does in Genesis 15 is promise Abraham that his offspring will constitute a vast number. At one level, God's promise is enough: "Abram believed the LORD, and he credited it to him as righteousness" (Gen 15:6). Abram's faith is simple and profound: he believed God's promises, taking God at his word. And that faith, in God's eyes, was credited as righteousness. This does not mean that Abram earned brownie points for deploying such a righteous faith. Rather, 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).
Yet however genuine this faith, some of the details of God's promise Abram has trouble imagining. God tells him of a time when his descendants will possess all the land around him, and Abram wavers and asks for a sign (Gen. 15:8). Graciously, God provides one: in a vision, Abram is enabled to see God entering into a covenant with him. Probably the pieces of the animals between which "a smoking firepot with a blazing torch" (Gen. 15:17) passes represent a way of saying, "May those who enter into this covenant similarly be torn apart if they break the terms of this covenant." What a visionary act of kindness to anchor Abram's faith is also an instance of God's long-range plans, his vast frame of reference: he is establishing his covenant with Abram and his offspring, a covenant relation into which Christians enter today (Gal. 3:6-9).
There is one more strand in this chapter that depicts God's long-term view of things. One reason why Abram cannot begin to take over the Promised Land immediately is that "the sin of the Amorites has not yet reached its full measure" (Gen 15:16). God's sovereign timing so matches his moral sensibilities that by the time the children of Abraham are ready to take over the Promised Land, the inhabitants of that land will have so sunk in degradation that judgment must be meted out. That time, God says, is coming, but in this chapter it has not yet arrived.