Frequently in Scripture, an oven or a furnace typifies intense suffering.
"Behold, I have refined you, but not as silver: I have tested you in the furnace of affliction." Isaiah 48:10
This applies at times to all of Gods people. You go into the furnace because the furnace does things for you that nothing else can do.
"He will sit as a refiner and a purifier of silver; He will purify the sons of Levi, And purge them as gold and silver, that they may offer to the Lord an offering in righteousness." Malachi 3:3
Precious metals are never purified without intense heat.
In the midst of this overwhelming darkness to which Abram was subjected - a darkness that was both natural and supernatural - there was
"a flaming torch which passed between these pieces"
What a depth of meaning there is in that! The flaming torch was a manifestation of the Spirit of God, corresponding to the
"the seven lamps of fire which are the seven Spirits of God" Revelation 4:5
John saw these before the throne in heaven. It was at this moment that the Lord, in the appearance of the flaming torch, made His commitment to Abram. He passed between the pieces and, in so doing, He entered into the covenant. This signifies Gods personal commitment to all mankind for all time on earth.