In this episode God comes to Abram and reaffirms his promise that he will become a great nation even though he is without a child and is a wonderer in a country that is not his own. God "cuts" a covenant with him and promises that if he is not faithful to this covenant He will be cut in two. This is a fascinating ritual that they practiced in Abram's day to show the seriousness of the agreement they were making. And so God makes this covenant with Abram to demonstrate the seriousness with which God is making this promise.