15:18 In that same day, the Lord made a covenant with Abram, saying, Unto thy seed have I given this land - He had said before, To thy seed will I give this land, but here he saith, I have given it; that is, I have given the promise, the charter is sealed and delivered, and cannot be disanulled. The possession is as sure in due time, as if it were now actually delivered to them. In David's time and Solomon's their jurisdiction extended to the utmost of these limits, 2Ch 9:26. And it was their own fault that they were not sooner and longer in possession of all these territories. They forfeited their right by their sins, and by their own sloth and cowardice kept themselves out of possession. The present occupants are named, because their number and strength and long prescription, should be no hindrance to the accomplishment of this promise in its season; and to magnify God's love to Abram and his seed, in giving to that one nation the possession of many nations.
15:17-21 The smoking furnace and the burning lamp, probably represented the Israelites' severe trials and joyful deliverance, with their gracious supports in the mean time. It is probable that this furnace and lamp, which passed between the pieces, burned and consumed them, and so completed the sacrifice, and testified God's acceptance of it. So it intimates that God's covenants with man are made by sacrifice, Ps 50:5. And we may know that he accepts our sacrifices, if he kindles in our souls pious and devout affections. The bounds of the land granted are stated. Several nations, or tribes, are spoken of, that must be cast out to make room for the seed of Abram. In this chapter we perceive in Abram faith struggling against, and triumphing over, unbelief. Wonder not, believers, if you meet with seasons of darkness and distress. But it is not the will of God that you should be cast down: fear not; for all that he was to Abram he will be to you.
