With the tenth and final plague, an angel of death is sent to pass through Egypt, killing all the firstborn sons. However, the Israelites are instructed to sacrifice a lamb and, in a very public statement, spread the lamb’s blood on the doorposts of their home. When the angel of death saw the blood of the lamb, he would pass over it, and the death of the lamb would take the place of the son.
This was a do-or-die proposition: If the Israelites refused to sacrifice the lamb, their firstborn sons would be lost. If they did sacrifice the lamb, the Egyptians would come after them. It was a dramatic invitation to trust that God would be faithful. This series of events is called the Passover — and it is a sign that reminds us to sacrifice the idols in our own lives, even if doing so seems impossible or has drastic consequences.
This final plague works. The Israelites leave Egypt, crossing through the Red Sea. Shortly after the Exodus, God renews His covenant with Moses and the entire nation, the people of Israel.