The tenth plague of Egypt (Exodus 12) leads to Passover, the first festival in the biblical calendar. Israel celebrates with Passover or Pesach, the beginning of a free life with the opportunity to build up their faith in God. The key to this story is in the first and perfect sacrifice.
God does not save because of ethnicity, but because of practiced faith. Faith is not about developing our ideas about God, but about listening to what He says.
The point is that the Egyptians trusted in other gods and despised the God of Israel. The attempts to wipe out Israel now hit them themselves.
Some think why should an animal be slaughtered, and the blood painted on the doorpost?
There are things in faith that we cannot explain as human beings because they come from a divine order, because they are important to God.
Perhaps it will help us if we remind ourselves that this story leads to the Jewish Passover festival. It was on this feast that Jesus, the perfect sacrifice, died. The death of Jesus is the fulfilment of Passover.