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.

Wesley's Notes

15:9 Take me an heifer - Perhaps Abram expected some sign from heaven, but God gives him a sign upon a sacrifice. Those that would receive the assurances of God's favour, must attend instituted ordinances, and expect to meet with God in them. Observe, God appointed that each of the beasts used for his service should be three years old, because then they were at their full growth and strength. God must be served with the best we have. We do not read that God gave Abram particular directions how to manage these, knowing that he was well verse d in the custom of sacrifices. Abram took as God appointed him, though as yet he knew not how these things should become a sign to him. He divided the beasts in the midst, according to the ceremony used in continuing covenants, Jer 34:18,19, where it is said, they cut the calf in twain, and passed between the parts. Abram, having prepared according to God's appointment, set himself to expect what sign God would give him by these.

Jamieson-Fausset-Brown Bible Commentary

9-21. Take me an heifer, &c.-On occasions of great importance, when two or more parties join in a compact, they either observe precisely the same rites as Abram did, or, where they do not, they invoke the lamp as their witness. According to these ideas, which have been from time immemorial engraven on the minds of Eastern people, the Lord Himself condescended to enter into covenant with Abram. The patriarch did not pass between the sacrifice and the reason was that in this transaction he was bound to nothing. He asked a sign, and God was pleased to give him a sign, by which, according to Eastern ideas, He bound Himself. In like manner God has entered into covenant with us; and in the glory of the only-begotten Son, who passed through between God and us, all who believe have, like Abram, a sign or pledge in the gift of the Spirit, whereby they may know that they shall inherit the heavenly Canaan.

Matthew Henry's Concise Commentary

15:7-11 Assurance was given to Abram of the land of Canaan for an inheritance. God never promises more than he is able to perform, as men often do. Abram did as God commanded him. He divided the beasts in the midst, according to the ceremony used in confirming covenants, Jer 34:18,19. Having prepared according to God's appointment, he set himself to wait for the sign God might give him. A watch must be kept upon our spiritual sacrifices. When vain thoughts, like these fowls, come down upon our sacrifices, we must drive them away, and seek to attend on God without distraction.