Similarly, (Exodus 12:13) "And the blood shall be for you as a sign, etc." Now how can the blood affect an angel or Israel? Rather, when Israel did this and placed the blood on their doors, the Holy One Blessed be He pitied them, viz. (Ibid. 23) "And the L–rd shall skip over the door."
When the Destroying Angel Passed Through Egypt That Night, It Would
Mekhilta Tractate Amalek 1:27