It fits with the time spent in Egypt, which is brought up next.
But I think it fits God as well. There's a sense in which it entails some terror for sinful beings to deal with God. The fire that passes through the animal pieces is not a cheery campfire. It comes to Abram with the word of the Only Holy God, and that is not something to take lightly. The promises are sweet, but the presence of God still feels ominous.
There are parallels to God's appearance on Mt. Sinai, with the fire imagery and the covenant announcement and all. Remember how that mountain too was scary and ominous. But our experience, says Hebrews, is different: "But you have come to Mount Zion and to the city of the living God, the heavenly Jerusalem, and to innumerable angels in festal gathering, and to the assembly of the firstborn who are enrolled in heaven, and to God, the judge of all, and to the spirits of the righteous made perfect, and to Jesus, the mediator of a new covenant, and to the sprinkled blook that speaks a better word than the blood of Abel" (Hebrews 12:22-24).
With Jesus as our mediator, the gloomy dread is gone for us who are in Christ. Not that we ever take God lightly. But we do find him wonderously, amazingly approachable.
And yes, that three hours of darkness on the cross made it possible. The only man for whom the presence of the Father should not have been dreadful—never, ever before had been dreadful—experienced it so that we can know the Father's welcome with all that gloomy darkness far removed.
