Genesis 1 and 2 show us God creating through a process of separating: light from dark, land from water, Isha from Ish. I think the pattern here in Genesis 15 is related.
But it’s Abram who cleaves the animals, and we might agree that this is a destructive act, rather than a creative one. However, we see that God dwells even in those separations, shown as a torch that passes between them. It’s quite powerful imagery: God in the spaces between.
I like to think that God healed those animals that were cleaved, and He brought them back to life so Abram could see that God is Lord over death and life as well.