How did Sarah and abraham show some faith and some disbelief in gods promises?

Sarah and Abraham demonstrated faith in God's promises by leaving their homeland and following God's command to journey to an unfamiliar land, trusting that they would become the parents of a great nation. However, their disbelief manifested when Sarah laughed at the notion of bearing a child in her old age and when Abraham tried to fulfill God's promise through Hagar, indicating doubt in God's timing and plan. Despite their moments of skepticism, they ultimately became key figures in the fulfillment of God's covenant.