Genesis 15:9
And he said unto him, Take me an heifer of three years old, and a she goat of three years old, and a ram of three years old, and a turtledove, and a young pigeon. And he said unto him, Take me an heifer of three years old, and a she goat of three years old, and a ram of three years old, and a turtledove, and a young pigeon.
God directed Abraham to bring five specific offerings for the covenant ceremony: a heifer three years old, a she-goat three years old, a ram three years old, a turtledove, and a young pigeon. Abraham cut the larger animals in two but left the birds undivided. Dividing the sacrifices and passing between the pieces was the customary form for ratifying a covenant.
By passing between the divided pieces, Abraham gave his solemn pledge of perpetual obedience. Afterward, visible tokens of divine presence passed between the pieces, thereby pledging the covenant on God's part. That divine act confirmed the promise of the land to Abraham's descendants.