In Genesis 15, when God appears to Abraham, Abraham pertly reminds God of His promise yet unfulfilled (15:2). After messing up with Hagar, he is much more humble when God speaks again in 17:1: he just falls on his face without saying anything (17:3). Our mouths are stopped and our words are fewer before God, when we know our sin more fully.
Back in chapter 15, God makes a self-imprecatory oath with him in the animals cut apart and the manifestation of God's presence in the pot going between the bleeding animal pieces. This was done in the culture (Jeremiah 34:18), as a statement that if I break the promise we have made, you may have my blood in death. God doesn't have Abraham walk through, only God does. The covenant is broken of course, for Abraham and all his descendants do not "walk before Me and be blameless" (Gen 17:3). And the blood of Jesus is spilled to cover it, and keep the bond between God and man, which was forged here.