God instructed Abram to bring animals for a covenant ceremony to affirm his promise of the land. Abram brought the animals and cut them in half, then waited as birds of prey came. As the sun went down, a deep sleep and darkness came over Abram. God then revealed to Abram that his descendants would be slaves in a foreign land for 400 years, a future fact they could later verify. This ceremony made the covenant between God and Abram unquestionable for generations to come.