‘And it about that when the sun went down, and it was dark, behold a flaming furnace and a flaming torch that passed between these pieces.'
The covenant is finalised and sealed. As elsewhere the flaming furnace and the flaming torch represent Yahweh Himself, although not directly. The mention of two signifies a twofold divine witness. We can compare the two angels who will be witnesses to the judgment of Sodom (Genesis 19) as Yahweh's representatives. Abram is not involved. This is a gift of God's grace.
The writer now summarises the covenant. The special nature of what has occurred is clear. Nowhere else is such a comment made on a theophany as ‘know of a surety'. He recognises the solemnity and totally unbreakable nature of what has happened. This can only indicate the end of the original tablet recording the covenant, finalising the extent of the promised land.