Genesis 15:10

He took unto him all these, and divided them in the midst.

This was the well-known method of preparing the animal for the ratification of. covenant. The Hebrew phrase, to make. covenant, means, etymologically, to "cut. covenant." The sacrificed victims were cut into two pieces, when ancient nations entered into. covenant, and the covenanting parties passed between them. "The division of the sacrifice into two is supposed to represent the two parties to the covenant; and their passing between the divided pieces to signify their union into one. In this case Abraham was there in person to pass between the pieces, and the manifested presence of God passed between them under the semblance of fire."

But the birds he divided not.

Again the custom of the law was set. According to the law (see Leviticus 1:17), fowls were not to be divided, but only cleft open that their intestines might be removed.