not much reflection today

What jumped out to me today is a verse that I find confusing. Having killed the requisite animals, Abram is hard at working keeping the birds of prey away, when, seemingly out of nowhere "a deep sleep fell upon Abram, and a deep and terrifying darkness descended upon him."

I'm guessing God put him to sleep, which would make sense. God was about to pass by as a flaming torch to consume all that Abram had offered, but why is the sleep that fell upon Abram called "a deep and terrifying darkness?"

I've decided to do some research, and it seems as though our Lectionary in its splitting verses (Gen 15.1-12, 17-18) has made for the confusion.

Here it is from the Lectionary:

As the sun was going down, a deep sleep fell upon Abram, and a deep and terrifying darkness descended upon him.

When the sun had gone down and it was dark, a smoking fire pot and a flaming torch passed between these pieces. On that day the LORD made a covenant with Abram, saying, "To your descendants I give this land, from the river of Egypt to the great river, the river Euphrates."

Here it is in context:
12 As the sun was about to set, a deep sleep fell upon Abram, and a great dark dread descended upon him. 13 And He said to Abram, "Know well that your offspring shall be strangers in a land not theirs, and they shall be enslaved and oppressed four hundred years; 14 but I will execute judgment on the nation they shall serve, and in the end they shall go free with great wealth. 15 As for you, You shall go to your fathers in peace; You shall be buried at a ripe old age. 16 And they shall return here in the fourth generation, for the iniquity of the Amorites is not yet complete." 17 When the sun set and it was very dark, there appeared a smoking oven, and a flaming torch which passed between those pieces. 18 On that day the LORD made a covenant with Abram, saying, "To your offspring I assign this land, from the river of Egypt to the great river, the river Euphrates:

God's promise in vv 13-16 isn't all good news; it isn't even mostly good news. The descendants of Abram will be oppressed in a foreign land for 400 years before they can enter the Promised Land. Surely this news is terrifying and dreadful to Abram. Just as God offers him the unfathomable news that he will sire an offspring he finds out that it is only for them to be brought very low for a very long time. Maybe that's where the dread and terror come from. Anyway, its an interesting verse, one suitable for further study.