How did Israel keep the death angel from killing their firstborn?
Israel escaped the death angel by faith: they applied the blood of the Passover lamb to their doorposts and remained inside their homes. When the angel passed through Egypt, every firstborn outside that blood-marked shelter died, but the death angel passed over those houses.
Les teaches that God had already made a division so the Jews no longer experienced the plagues that fell on Egypt, but the final plague—the death of the firstborn—was the worst and struck families and parents. The angel would fly over, and every house in Egypt would lose its firstborn, even the livestock. Israel had an out, but it depended on faith: they had to put the blood of the Passover lamb on the doorposts and stay within the safety of their home. Then the death angel would pass over. Les notes this began the Passover the Jews still celebrate in the spring, and he distinguishes Passover from Atonement or Yom Kippur. He also says Christ is our Passover, and the Passover aspect is the protection given by the blood of the Lamb.