Yafles Netiv L'Afo. Rabbi Huna in the name of Rabbi Ivon says that every blow that was inflicted on the Egyptians was measured and weighed, and it was inflicted upon them accordingly. Their souls were not spared from death. Another explanation: Rabbi Yehoshua ben Levi said that every blow that was inflicted upon them was a specific punishment for a specific sin.
And they survived only because of God's protection. And all the firstborn in Egypt were struck. Rabbi Abba bar Acha says that the firstborn refers to the firstborn son of a man, the firstborn daughter of a woman, the firstborn of an animal, and the firstborn of everything. And if someone did not have a firstborn, the death of someone else in their household served as atonement, as it is stated: "For there was no house where there was not someone dead" (Exodus 12:30)....