Sforno on Exodus 12:13/ספורנו על שמות י״ב:י״ג

1ולא יהיה בכם נגף למשחית, so you will not be struck with a plague as a corollary to the retributive action I am taking against Egypt.

2בהכותי, G’d caused other harm to the Egyptians during that night, in addition to killing all their firstborn. Had it not been for the “passing over” He had performed as an act of pity for the Israelites, they would not have escaped that judgment even if their firstborn had not been killed. The matter is similar to what the angel had told Lot concerning his not turning around, when he warned פן תספה בעון העיר, “lest you will be wiped out on account of the guilt of the people inside the city.” (Genesis 19,15) G’d commanded the Israelites to smear the blood as a sign so that they would escape. This was for the sake of His great name, as we know from Ezekiel 20,9 when the prophet reminded the people that G’d had said בדמיך חיי, בדמיך חיי, ”by your blood you shall live, by your blood you shall live.”(Ezekiel 16,6) [both the blood of the circumcision and that of the Passover lamb. Ed.]