Together with the final plague of smiting the firstborn, G-d also warns that the Jews should not venture out that night and must place blood on their doorposts and doors.
“And you shall take a bunch of hyssop and immerse [it] in the blood that is in the basin, and you shall extend to the lintel and to the two doorposts the blood that is in the basin, and you shall not go out, any man from the entrance of his house until morning. The Lord will pass to smite the Egyptians, and He will see the blood on the lintel and on the two doorposts, and the Lord will pass over the entrance, and He will not permit the destroyer to enter your houses to smite [you].” (12:22-3)
Rashi (12:22), citing the Mechilta, explains that “... once permission is given to the destroying angel to wound he makes no distinction between righteous and wicked, and nighttime is the domain of the destroying agencies ...”
Commentators are bothered by this warning about the destroying angel considering that the Torah tells us that it was G-d Himself (12:29), who eliminated the firstborn. So why the concern about the destroying angels.
Bartenura suggests that G-d dealt with the actual firstborns. However on that night, partial firstborns (to one parent, for example) and heads of households were also killed. These were handled by destructive angels. And Bartenura proves this since G-d struck at midnight precisely and yet the Jews were warned not to leave all night.
In a similar vein, Maskil L’Dovid suggests that the destroyers were given license on the night and all were fair game.
Extending this thought, Sifsei Chachomim explains that had Jews been harmed that night, then Egyptians would have pointed out that there was nothing special as Jews were also affected.
Meshech Chochma raises an interesting point.
In truth, the Jews in Egypt were in most ways no different to the native population – they didn’t observe Torah or Mitzvos. Therefore, they too were in danger when the destruction of the firstborns was taking place.
But they did keep their Hebrew names, clothing and language and that kept them separate from the Egyptians to the point that only one Jewish woman was known to have had a physical relationship with an Egyptian and that was inadvertent.
In contrast the Jews exiled to Babylon kept Torah but did not keep their Hebrew names, dress or language. But fast forward a mere seventy years later, they had intermarried and lost their unique Jewishness.
It is the little distinguishing features and customs such as the Rabbinic decrees about wine, oil, bread, cooked foods, that allowed the Jews to remain separate.
IN OUR DRIVE TO INTEGRATE into the cultures that we live in, it is still critical for us to maintain the small things that make us different from our neighbours. And those differences need to be passed to out children and through the generations otherwise we, as a people, risk disappearing.
