Gen 15 17 When the sun had set and darkness had fallen, a smoking firepot with a blazing torch appeared and passed between the pieces. 18 On that day the LORD made a covenant with Abram and said, "To your descendants I give this land, from the river ^F74 of Egypt to the great river, the Euphrates-19  the land of the Kenites, Kenizzites, Kadmonites,20  Hittites, Perizzites, Rephaites,21  Amorites, Canaanites, Girgashites and Jebusites."

 In the OT the phyiscal events were ordered by Gods creative work in the law, covenants, statutes, decrees, curses and promises. When the sacrifice was instituted it was a ceremony of violence and provision. The sacrifice was not only put to death but it was slaughtered. If the physical act of sacrificing automatically forced God to bless the recipient in the gift then we could argue that Gods blessing is contained in a physical object. But if it was an illustration of the eternal work of God that the blessing would come out of Gods pronouncements. This is why the pronouncement of cursing is illustrated in slaughtering the animal. So the when prophets teach by illustrations they are pointing to Gods eternal pronouncements that are made from heaven in order to establish He government. In some ways when the Prophets spoke the curses they were using the eternal violence of God that was demanded in slaughtering the animal.

This is why the Psalmist distinguishes between an acceptable sacrifice and an evil sacrifice. The distinguishing factor of an acceptable offering was in the Prophets practice of speaking the law, covenants, statutes, curses etc. So we find this illustration used by God to show Abram that He judge the nations in order to take the spoils and bless the offspring of Israel. We could say that the sacrifice was not just a religious observance. But it was the illustration that God governs the nations by overcoming their threats from His throne. God does this through the prophets who pronounce the curses upon law breakers. God had to overcome the violence of the nations in order to establish His covenant wit h Abraham. He overcome them by a direct pronouncement from His throne. He is teaching that Gods blessing is obtained by pushing  the curse of the wicked underneath the feet of His prophets in the curse of the law. The animal had  to be slaughtered.