Abram was 75 years old when God made the great promise to him (12:1-4). By chapter 15 several years had passed and none of the promises had come true. Abram had no children. He lived in tents, and didn't even have a small patch of land that was his own. It was at this time that God spoke to him and calm his uncertainty. And God knew that amidst Abram's uncertainty (15:2-3) he was still righteous before God (15:6).