Matthew Poole and continuators on Genesis 15:17

17. And it came to pass that when the Sun went down, and it was dark, behold a smoaking furnace, and a burning lamp that passed between those pieces.

By which symbol God designed to represent, either 1. The future state of Abram's seed: the smoaking furnace, signifying Israel's misery in the iron furnace of Egypt, as it is called, Ier. 11. 4. and the burning Lamp, noting their deliverance, or light shining out of darkness, Or, 2. His own presence: for God is called a consuming fire, Heb. 12. last, and both smoak and fire are elsewhere mentioned as the signs and means of God's appearance. See Exod. 3. 2. and 19. 9, 16, 18. and 20. 18. And this sense seems to be favoured by the following words, it being the custom of persons entring into covenant to pass between such pieces, as hath been said: and because God hath no body which could visibly do so, therefore he doth it in this type or shadow.

Marginal references: Heb. a lamp of fire.