Genesis 15:12 - Coke's Commentary on the Holy Bible

And when the sun was going down— The original is, and the sun was (לבוא labo, ad intrandum, says Montanus) about to enter, "the time of sun-rising approached," which I take to be the true sense of the passage. For, as I conceive, God came to Abram in the night, perhaps the beginning of it; after which he brought him forth, and ordered him to count the stars, if possible, Genesis 15:5. This done, he employs him in preparing this sacrifice; by which time morning drew near, "the sun was about to enter:" when Abram, fatigued with the business in which he had been employed, and wanting rest, fell into a deep sleep: then, as the sacred writer expresses it, an horror of great darkness fell upon him, or was represented in vision to him; the meaning of which is fully and clearly explained in the next verse.