This is the language of Rashi (Shemot 10:22): "And why did He bring darkness upon them? Because there were wicked people among Israel in that generation who did not want to leave, and they died during the three days of darkness so that the Egyptians would not see their downfall and say, 'They are also being struck like us.' Moreover, the Israelites searched and saw their vessels, and when they went out and asked them, they would say, 'We have nothing,' and he would say to him, 'I saw it in your house, and it is in such-and-such place.' End of quote."

From his words, we learn that the plague of darkness came upon the Egyptians for the benefit of Israel. Indeed, in the Midrash (Shemot Rabbah, Parasha 14, Siman 1), it is written in this language: "And the Lord said to Moshe, 'Stretch out your hand towards the heavens' (Shemot 10:21) – this is what is written (Tehillim 105:28), 'He sent darkness, and it was dark, and they did not defy His word.' Our Rabbis said: Because they did not accept the sovereignty of the word of the Holy One, blessed be He, upon them. Another explanation: The Holy One, blessed be He, said to the angels, 'The Egyptians are worthy of being struck by darkness,' immediately they all agreed as one and did not defy. End of quote." And similarly, it is stated in Midrash Tanchuma (Bo, Siman 4): "They did not return, they imprisoned them in the house of darkness, as it is said (Shemot 10:22), 'And there was thick darkness.'"

It is explained that the plague of darkness came to punish the Egyptians. For the first reason in Rashi, it needs clarification why those who died were called wicked. This matter is explained in the Midrash (Shemot Rabbah, Parasha 14, Siman 3): "Why did He bring darkness upon them? Blessed be the name of the Holy One, blessed be He, who shows no favoritism and examines the heart and tests the kidneys. Because there were criminals among Israel who had patrons among the Egyptians, and they had wealth and honor there, and they did not want to leave. The Holy One, blessed be He, said, 'If I bring a public plague upon them and they die, the Egyptians will say, just as it passed over us, so it passed over them.' Therefore, He brought darkness upon the Egyptians for three days so that they would be burying their dead, and their enemies would not see them." This means that their wickedness was the very fact that they did not want to leave Egypt.

Accordingly, the words of the Rosh (Shemot 10:10) align well: "One may ask, why did all the wicked die during the three days of darkness, but Dathan and Abiram did not die, who were outright wicked? One can say, even though they were wicked, they did not despair of the redemption." This means that even a wicked person could leave Egypt, provided he believed and wanted to be redeemed.

However, in another place (Bamidbar Rabbah, Parasha 15, Siman 12), the Midrash explains another reason: "Even the tribe of Levi dedicated themselves to sanctifying the name of the Holy One, blessed be He. For when Israel was in Egypt, they despised the Torah and circumcision, as Yechezkel rebukes them (Yechezkel 20:5): 'Thus said the Lord God on the day when I chose Israel and lifted My hand to the seed of the house of Yaakov and made Myself known to them in the land of Egypt.' What is written afterward (ibid. 8): 'But they rebelled against Me and would not listen to Me [etc.], and I said to pour out My wrath upon them.' What did the Holy One, blessed be He, do? He brought darkness upon the Egyptians for three days and killed all the wicked among Israel, as it says (ibid. 38): 'I will purge from among you the rebels and those who transgress against Me.' And it says (Shir HaShirim 2:13): 'The fig tree has formed its fruit' – these are the wicked among Israel. 'And the vines in blossom give forth fragrance' – those remaining who repented were accepted." This implies that those who left were worthy of leaving.

However, it is difficult to reconcile this with what is found in the Yalkut Shimoni (Beshalach, Remez 234): "'And the waters were a wall unto them' (Shemot 14:22) – Samael descended and said before Him: 'Master of the Universe, did not Israel worship idols in Egypt? And You are performing miracles for them.'" This implies that even those who left were not worthy of a miracle. However, the Midrash immediately answers this: "Immediately the Holy One, blessed be He, replied to him: 'Fool of the world, did they worship it willingly? Did they not worship it out of coercion and mental distress? And you judge the mistaken as intentional and the coerced as willing.'"

Similarly, the Rambam rules (Chapter 5 of Hilchot Yesodei HaTorah, Halacha 4): "Anyone about whom it is said 'he should be killed and not transgress,' and he transgressed and was not killed, he desecrates the name of God, etc. Nevertheless, because he transgressed under duress, he is not lashed, and it is needless to say that he is not executed by the court, even if he killed under duress, he is not lashed nor executed except for one who transgresses willingly, with witnesses and warning, etc. And if idolatry, which is the gravest of all, if one worships it under duress, he is not liable for karet, and it is needless to say death by the court. How much more so for other commandments stated in the Torah. But if one can save himself and escape from the hand of the wicked king and does not do so, he is like a dog that returns to its vomit, and he is called an intentional idol worshiper and is banished from the world to come and descends to the lowest level of Gehenna."

It follows that Israel, who worshipped idols under duress and out of subjugation, are not liable for punishment, especially since when the time came to save themselves from the hand of the wicked king and to be free from coercion, they did so immediately. Therefore, they were not liable to be punished with the Egyptians at the Red Sea. And they also repented for their rejection of the Torah and circumcision, and their repentance was accepted.

In this way, it aligns well with Rashi's explanation that they died because they did not want to leave, and in the Midrash, it is explicitly stated that they died because of other transgressions. As long as they were subjugated, they committed transgressions under duress and mental distress. But now, when the way was opened for them to escape from subjugation and distress, and consequently to distance themselves from sin, and they did not want to leave, they died during the days of darkness.

Still, one may ask, why not exempt those wicked ones from punishment as we would for a child who was captured, according to the opinion of the Chazon Ish (see his words in Yoreh Deah, Siman 2, Se'if Katan 28), that without teachers, one has the status of a captured child. Perhaps this status was nullified after they saw with their own eyes the wonders of God in the Ten Plagues.

Furthermore, it can be explained that part of the reason why some of Israel died during the plague of darkness is because they distanced themselves and did not include themselves among the community of Israel. The entire essence of the Korban Pesach is the unity among all Jews, as implied by the verses (Shemot 12:3-4): "Speak to the entire congregation of Israel, saying: On the tenth of this month, each one shall take a lamb for their father's house, a lamb for a household. And if the household is too small for a lamb, he and his neighbor who is near his house shall take one according to the number of souls, each one according to his eating shall make your count for the lamb." And later (ibid. 47): "The entire congregation of Israel shall keep it." And Yonatan translated: "All the congregation of Israel should mix with each other, family with another family, to perform it." Whereas those wicked ones fulfilled in themselves: 'And no one saw his brother,' and they wanted to continue their lives under the hand of the Egyptians, with all the pleasures they had and the sins they had committed until then, and they did not draw near to the community of Israel who prepared themselves for the exodus and redemption. Therefore, they were punished to die in the plague of darkness and were not redeemed from Egypt.