Charles Ellicott Commentary Genesis 15:17

"And it came to pass, that, when the sun went down, and it was dark, behold, a smoking furnace, and a flaming torch that passed between these pieces." — Genesis 15:17 (ASV)

A smoking furnace. The word really means the circular firepot that Eastern peoples use in their houses to sit around for warmth. This one was wreathed in smoke, from which shot a burning lamp (Hebrew, a torch of flame). For not two symbols, but only one, passed between the divided carcasses. Abram had probably passed between them immediately after arranging them, and now Jehovah does the same. Fire is the recognized symbol of the Deity, as in the burning bush, the pillar of fire, the lightnings on Mount Sinai, etc.