How did Abraham demonstrate faith in God's promises?

In Genesis 17:17, Abraham's laughter is expressed as joy in belief rather than disbelief. His falling on his face indicates both humble reverence and delight in God's promise. Abraham's faith is foundational to his relationship with God—it is through faith that he receives the promise of a son, despite the apparent impossibility given his and Sarah's age. This act exemplifies the nature of faith whereby believers trust in God's ability to fulfill His promises regardless of circumstances, emphasizing a key aspect of sovereign grace.