As a sign to offer reassurance about the future to Abraham, the LORD utilizes an Ancient Near Eastern custom involving the cutting-in-two of animals to symbolize the seriousness of the covenant should anyone break it.
In addition, God explains the upcoming 400 years of sojourning in Egypt that Abraham's descendants will endure in part because his wrath against the Canaanites is not yet ready because theirs sins have not yet reached the "full measure." This has implications for how we understand God's judgment against sin and evil here in this life.