And he said to him, “I am the LORD who brought you out from Ur of the Chaldeans to give you this land to possess.”  But he said, “O Lord GOD, how am I to know that I shall possess it?”  He said to him, “Bring me a heifer three years old, a female goat three years old, a ram three years old, a turtledove, and a young pigeon.”  And he brought him all these, cut them in half, and laid each half over against the other. But he did not cut the birds in half.  And when birds of prey came down on the carcasses, Abram drove them away.
 As the sun was going down, a deep sleep fell on Abram. And behold, dreadful and great darkness fell upon him.  Then the LORD said to Abram, “Know for certain that your offspring will be sojourners in a land that is not theirs and will be servants there, and they will be afflicted for four hundred years.  But I will bring judgment on the nation that they serve, and afterward they shall come out with great possessions.  As for you, you shall go to your fathers in peace; you shall be buried in a good old age.  And they shall come back here in the fourth generation, for the iniquity of the Amorites is not yet complete.”
 When the sun had gone down and it was dark, behold, a smoking fire pot and a flaming torch passed between these pieces.
– Genesis 15:7-17
Abram trusts God and is following him by faith, but still he wonders how he can be certain that God will fulfill His promises. If God’s promises were things that Abram could control or accomplish on his own, he might not have so many questions, but God promises things beyond Abram’s wildest dreams.
In response to Abram’s question, God instructs him to cut animals in half and lay them out on the ground. To us this a strange response, but Abram would have readily recognized this to be a covenant ceremony, a common custom in the Ancient Near East. In a covenant ceremony, two participants agree to stipulations (what they must do), rewards, and punishments. They then walk between the pieces of animals torn in two, essentially saying, “If I am not faithful to the covenant, may I be torn in two just as these animals.”
After God reiterates His promises, a smoking fire pot and a flaming torch pass between the pieces. Abram does not walk through, only God. God is saying, “May I be torn in two if these things do not pass.” God does not make idle promises. He has never spoken an empty word. He will not be thwarted by human incompetence or rebellion. God is certain to fulfill His promises because they depend not on Abram but on God.