In some way this is a perplexing verse, but it is vital. Abram ‘said, Lord GOD’ – this is the first chapter to contain this address to God, ‘Lord GOD, whereby shall I know that I shall inherit it?’ How can I be certain? He had faith.
Whatever can he learn from that? God is going to give him an issue which will lead to an enormous number of descendants through which Christ will come; that is the promise of Genesis 3:15. And God is going to ratify this promise and in the meantime God keeps him waiting, and the birds of prey attack the carcasses, and Abram must drive them away. He is going to learn that he and his prophetic successors, will be the guardians of God's revelation. He is being given a prophecy. This is going to pass into holy Scripture: all that Abram has been taught. There will be attacks upon the church of God. Down through Old Testament history and by extension the church age, the people of God have got to continuously drive off the birds of prey and keep the cause of Christ pure and intact.