Summary: God’s delays are not denials. God will not fail to fulfil that which He has promised.
THE CERTAINTY OF THE PROMISE
The priest-king Melchisedec knew God Most High, maker of heaven and earth (Genesis 14:18-19). This same God had led Abram out of his father’s house, and now identified Himself as “the LORD” - the One who was, and is, and continues to be (Genesis 15:7). Such a God could not, would not, fail to accomplish the thing which He had promised: a land, and offspring to inhabit it.
“How shall this be?” Abram reverently enquired (Genesis 15:8). The father of the faithful was not afraid to engage in familiar conversation with the LORD. However, we must be careful how we question God: the unreasonable and impertinent doubt of Zacharias brought temporal judgement, albeit temporarily (Luke 1:18-20); whereas the humble and honest questioning of Mary brought reassurance (Luke 1:34, 38).
The answer of the LORD came first with a visual aid, but also with words. The visual aid was the cutting of a covenant (Genesis 15:9-11; Genesis 15:17). The words spoke of things to come which gave Abram more than a little sense of foreboding (Genesis 15:12-16), but which would all work out in the end (Genesis 15:18-20).
First of all, five sacrifices were required (Genesis 15:9). These were divided between the parties to the covenant, which indicates to us that there is no communion with God without the shedding of blood (Genesis 15:10). From one night (Genesis 15:5) to the next (Genesis 15:17), Abram guarded the sacrifices from scavenging birds (Genesis 15:11) - just as surely as we must watch over our spiritual praise and sacrifice, that it does not become tainted by the distractions of the world.
Then Abram slept, and was all but engulfed by the sense of foreboding that came upon him (Genesis 15:12). The LORD spoke of the certainty that Abram would have offspring as promised - but informed him that his seed would be in captivity in another land for 400 years (Genesis 15:13), before they would at last be delivered and come out with great substance (Genesis 15:14). As for Abram, he would go to his fathers in peace (Genesis 15:15) - indicating the continuity of fellowship after death (Matthew 22:32).
The reason given for God not immediately consuming the inhabitants of the land was that their iniquity “was not yet full” (Genesis 15:16). This is the Lord’s patience: He is not willing that any should perish, but His coming is delayed to give the greater number of people the greater opportunity to repent (2 Peter 3:9). Perhaps God’s suffering people are standing in the breach “between the dead and the living” (Numbers 16:48) just so that those who are “dead in trespasses and sins” (Ephesians 2:1) do have the opportunity to “choose life” (Deuteronomy 30:19).
The parties to man-made treaties customarily passed between the pieces of their sacrifices, invoking to themselves a curse to the effect of “may the gods do so to me, and more also” (1 Kings 19:2) - as is illustrated in the case of Zedekiah’s broken covenant (Jeremiah 34:18-19). When it came to the time for the parties of the God-initiated covenant to pass between the pieces, the fire of God’s presence passed through alone (Genesis 15:17). The LORD thereby pronounced that, if His covenant was broken, He would bear the penalty alone - and He did in fact take the curse of it, our curse, upon Himself in the person of our Lord Jesus Christ (Galatians 3:13-14).