What does the Bible say about God's promises to Abram?

In Genesis 15, God makes a significant promise to Abram, assuring him that his heir would come from his own body. Despite the passing years and Abram's doubt due to his age and Sarah's barrenness, God remains faithful. In Genesis 16, we see Abram and Sarah’s misguided attempt to fulfill God's promise through Hagar, illustrating human unbelief contrasted with Divine promise. Throughout the narrative, God’s promise of an heir stands firm, reminding us that His plans are not thwarted by our failures. This underscores a core theme in Reformed theology—God's sovereign grace and faithfulness, which ensure that His purposes will be accomplished.