What does Abraham presenting Sarah as his sister (Genesis 12 and 20) teach Christians about reconciling fear and faith?

In Genesis 12:10–20, during a famine, Abraham (Abram) goes to Egypt and tells Pharaoh that Sarah is his sister because he fears he will be killed on account of her beauty. Pharaoh takes her into his house, and God intervenes by sending plagues before she is returned. Later, in Genesis 20:1–18, Abraham again identifies Sarah as his sister while sojourning in Gerar. King Abimelech takes her, and God warns him in a dream, after which Sarah is restored to Abraham. Given that Abraham is later commended in Scripture as a model of faith (e.g., Romans 4; Hebrews 11), how should Christians understand these repeated episodes? What do these narratives teach about the relationship between fear and faith in a believer’s life?