“Your lamb shall be without blemish, a male a year old…” (v5). In Egypt, the Israelites only had circumcision and their ethnic descent (from Abraham, Isaac, and Jacob) to unite them. The Passover celebration – symbolizing their rescue out of Egypt and escape from the angel of death – was the first ritual God commanded them to do yearly. Eating the roast lamb “with sandals on their feet” (v11), with unleavened bread, and putting its blood on their doors all communicated: God is our Rescuer.
God defined Himself as “the One who brought you out of Egypt” before giving the Law. He is the One who initiates salvation; we love Him because He first loved us.