7 And he [God] said unto him [Abram], I am the Lord that brought thee out of Ur of the Chaldees, to give thee this land to inherit it.
8 And he said, Lord God, whereby shall I know that I shall inherit it?
9 And he said unto him, Take me an heifer of three years old, and a she goat of three years old, and a ram of three years old, and a turtledove, and a young pigeon.
10 And he took unto him all these, and divided them in the midst, and laid each piece one against another: but the birds divided he not.
11 And when the fowls came down upon the carcases, Abram drove them away.
12 And when the sun was going down, a deep sleep fell upon Abram; and, lo, an horror of great darkness fell upon him.
13 And he said unto Abram, Know of a surety that thy seed shall be a stranger in a land that is not theirs, and shall serve them; and they shall afflict them four hundred years;
14 And also that nation, whom they shall serve, will I judge: and afterward shall they come out with great substance.
15 And thou shalt go to thy fathers in peace; thou shalt be buried in a good old age.
16 But in the fourth generation they shall come hither again: for the iniquity of the Amorites is not yet full.
17 And it came to pass, that, when the sun went down, and it was dark, behold a smoking furnace, and a burning lamp that passed between those pieces. (Genesis 15:7-17)
In order to certify that His promises to Abram would be fulfilled, the Lord told Abram to take a heifer, a nanny goat, a ram, turtle dove, and a pigeon to cut a covenant with him. The covenant of this sort was made by cutting the animals in half, and both parties to covenant walked between the two pieces. It was to demonstrate the kind of death that would happen if either party broke the covenant. It is interesting that the Lord doesn’t have Abram cut up just one animal, but three. I suppose this is to make a point about how serious the Lord is about keeping this promise.
So Abram prepares the animals, but the Lord doesn’t show up right away, so Abram has to drive away the vultures from the animal parts.
In v12, something happens that is puzzling. When the sun goes down a deep sleep falls on Abram along with a horror of great darkness. What was this?
I suspect that was Satan trying to prevent Abram from going through with this covenant with the Lord. Satan does not like people to make covenants with God, and tries to disrupt impending spiritual experiences in any way he can. (This fits very well with the opposition Satan hit Joseph Smith with before the first vision, as well as the opposition Moses faced when having his vision.) Satan could have attacked Abram with thoughts that the delay of waiting for the Lord meant that the Lord had changed His mind. He could have also tried to scare Abram away by suggesting that once he made this covenant he’d be stuck and any little deviation would put him in Satan’s power.
Even though we do not have the details recorded, Abram would have had to call on the Lord for strength to resist. And in the process, he was filled with the Holy Ghost, which seems to have filled him with the spirit of prophecy and he was inspired to know what would happen to his posterity up to four hundred years in the future.
And finally the Lord came, like a smoking furnace and a burning lamp, and passed through the pieces to confirm the covenant.
Once I read between the lines, this story reinforces the principle that there is opposition in all things. Satan was at work trying to disrupt Abram’s faith just as much as he is at work today. The solution is to pray always.