So he brought him all of these and cut them down the middle and laid each half opposite the other, but he did not divide the birds. Bible

“cut them down the middle.” There were many different ways of making a blood covenant in the ancient world—although there were always some similarities, the exact way the covenant was made differed somewhat from place to place and through time. One of the ancient ways to make a blood covenant was to cut the animals in half, after which the parties making the covenant would walk between the bloody pieces (or, in the case of birds, between the bloody animals). This method was obviously practiced in the time of Abraham, and it was still in practice over 1000 years later (Jer. 34:18). This particular covenant God made was unique because ordinarily both parties to the covenant would walk between the pieces, but in this case God put Abraham to sleep and made a covenant with himself; it was just a smoking firepot with a flaming torch, symbols that represented God, that went between the halves of the sacrifice. Thus, in effect, God made the covenant with Himself and so did away with the possibility of “human error.” In other words, by making the covenant with Himself, God was guaranteeing that Abraham and his descendants would get the Promised Land (cp. Gen. 15:8). God did not want Abraham’s descendants breaking any terms of the covenant and forfeiting the right to the Promised Land.

Commentary for: Genesis 15:10