A deep sleep fell upon Abram; partly natural, from his labour in killing and sacrificing those creatures; and partly sent upon him from God, to make way for the following representation. He seemed to be covered with a dreadful darkness, which was either,
1. A token of God's special presence: compare 1 Kings 8:12. Or,
2. A signification of the distressed and doleful condition of Abram's seed; for darkness in Scripture is frequently mentioned as an emblem or sign of great misery, as Psalms 88:6, Psalms 107:14, &c.