“And every firstborn in the land of Egypt will die, from the firstborn of Paroh who sits on his throne to the firstborn of the servant woman who is behind the millstones, and every firstborn animal.” (Shemot 11:5)
Moshe warns Paroh that if he continues to refuse to release Bnai Yisrael, Hashem will bring upon him and his nation the plague of the firstborn. Moshe describes to Paroh the scope of the plague. All of the firstborn will be killed. The plague will extend from the most exalted households in the land – Paroh’s own household – to the most humble households – the households of servants. Even the firstborn animals will not be spared.
Rashi comments on this passage: “…to the firstborn of the captive.” Why were the captives smitten? So that they would not say, “Our deity has demanded [vengeance] for their [our] degradation, and brought retribution upon Egypt.” Rashi is explaining the reason that the families of captives in Egypt were included in the plague. He explains that the captives were included in order to assure that the significance of the plague would not be misunderstood. Like Bnai Yisrael, these captives were also afflicted by the Egyptians. These captives might be tempted to attribute the plague to their own deities. Perhaps, they would assert that their deities had brought the plague upon the Egyptians in order to avenge their suffering. In order to negate this fallacious claim, even the firstborn of these captives were killed by the plague.
There is an obvious problem with these comments. The passage actually makes no mention of the inclusion of the firstborn of the captives in the plague! The Torah does indicate that these firstborn were included in the plague. However, the passage that describes their inclusion is in the next chapter.
“It came to pass at midnight, and Hashem struck every firstborn in the land of Egypt, from the firstborn of Paroh who sits on his throne to the firstborn of the captive who is in the dungeon, and every firstborn animal.” (Shemot 12:29)
This passage describes the actual events of the plague of the firstborn. The passage confirms the scope of the plague. It extended from the household of Paroh to the households of captives in the land of Egypt. In this passage the captives, to whom Rashi referred, are mentioned.
In this passage, Rashi again discusses the inclusion of the households of the captives in the plague. Rashi makes two points: He explains that the servant woman mentioned in the earlier passage is not the same person as the captive described in this latter passage. In other words, “servant woman” and “captive” are not alternative descriptions of the same person. Rashi also returns to the issue of the inclusion of the captives’ households in the plague. Why were these households included? Rashi recounts the explanation he offered earlier: The inclusion of these households in the plague assured that these captives could not attribute the plague to their own deities. However, in this instance, Rashi offers a second explanation for the inclusion of the captives’ households. He explains that these captives rejoiced in the subjugation and affliction of Bnai Yisrael. In order to punish them for this mean-spirited, baseless hatred, their firstborn were included in the plague.
This raises a second problem: In Rashi’s initial discussion of the inclusion of the captives in the plague, he offered a single explanation. They were included in order to preclude any attribution of the plague to their own deities. However, in Rashi’s subsequent treatment of the issue, he offers a second explanation for their inclusion: They were included as a punishment for their baseless hatred of Bnai Yisrael. Why does Rashi not include this second explanation in his initial treatment of the issue? Why does Rashi introduce this second explanation only in his subsequent return to the issue? In order to answer these questions, we must consider a further comment by Rashi.
“Moshe said, “So said Hashem: Near midnight, I will go out into the midst of Egypt.” (Shemot 11:4)
In this pasuk, Moshe reveals to Paroh the hour at which the plague of the firstborn will take place. The commentaries dispute the exact translation of the passage. Rashi suggests that the proper translation is that “near midnight” the plague will befall the Egyptians.
Rashi recognizes that this translation presents a problem: It is odd that Moshe described the moment of the plague’s onset as “near midnight.” Certainly, Hashem would initiate the plague at the exact moment He desired! In fact, in the next chapter – in describing the actual events of the plague – the Torah tells us that the plague began at precisely midnight. Why did Moshe tell Paroh that the plague would begin “near midnight”?
Rashi responds that Moshe was reluctant to specify the precise moment of the plague’s onset. Paroh’s astronomers might attempt to calculate the exact moment of midnight. If their calculations were marginally imprecise, the plague would either precede or follow the moment they had calculated as the time for its foretold onset. These astronomers would not consider the possibility that their calculations were in error. Instead, they would claim that Moshe had not been correct in his pronouncement. In order to avoid this accusation, Moshe declined to indicate the precise moment of the plague’s onset, and instead, provided an approximate time. So, if the astronomers incorrectly concluded that the plague began a few moments before or after midnight, this would not contradict Moshe’s prophecy or undermine his credibility.
Let us consider Rashi’s comments more carefully. According to Rashi, Moshe introduced an approximation – near midnight. He did this in order to assure that there would be no mistake regarding the accuracy of his prophecy. But why was this important? Why did Moshe feel that it was imperative that Paroh and the Egyptians recognize that his prophecy was completely accurate?
Apparently, Moshe concluded that it was important that there be no confusion regarding the nature of the plague. Paroh and the Egyptians were to understand the plague as Divine retribution. Moshe insured that there would be no confusion regarding the providential nature of the plague by foretelling the event. However, Moshe recognized that his prophetic revelation of the plague would only be meaningful if it was completely accurate. If Moshe’s prophecy was perceived as inaccurate or flawed, Paroh and the Egyptians would be tempted to deny the authenticity of Moshe’s prophecy. They would argue that a flawed prediction could not be actual prophecy. If Moshe’s prophecy was discredited, then the providential nature of the plague could also be denied.
Now, we can answer our first question. We noted above that Rashi initially discussed the captives on a passage 11:5. But, the passage does not mention these captives. The inclusion of these households is first noted by the Torah in the following chapter. In order to answer this question, it is important to appreciate that Rashi’s initial comments regarding the captives directly follow his explanation of Moshe’s use of the phrase “near midnight.” This juxtaposition provides a context for Rashi’s comments regarding the captives.
It appears that Rashi includes these comments at this point in order to respond to a question. Moshe provided an approximate time for the onset of the plague in order to assure that the plague would be recognized as Divine retribution. How did Moshe know that it was important to communicate to Paroh and the Egyptians that the plague was providential? Rashi is responding to this question. Moshe knew that the plague would extend to the households of the captives. He understood the reasons for their inclusion in the plague. They were included in order to preclude any misunderstanding regarding the origin of the plague. These captives would not be able to attribute the plague to their own deities. Only Bnai Yisrael would be protected from the devastation. Only Hashem – the G-d of Bnai Yisrael – could be the source of this punishment. Moshe concluded that a fundamental element of the plague was its manifest origin. Moshe understood that his prophecy was another means of demonstrating the Divine origin of the plague. Therefore, he constructed his prophecy in a manner that conformed to this objective. Through this adaptation of the prophecy, he assured that its credibility would not be undermined.
Now, let us consider our second question. In Rashi’s second treatment of the inclusion of the captives in the plague, he offers two explanations. Only one of these explanations is included in his first treatment of the issue. The above analysis suggests a simple solution to this problem. In his initial comments, Rashi’s intention is limited to providing an explanation for Moshe’s actions. Rashi wishes to explain Moshe’s basis for introducing an approximation into his prophecy. Rashi is not interested in enumerating all of the factors that dictated the inclusion of the captives in the plague. The captives were included in the plague for two reasons: First, Hashem wanted the origins of the plague to the manifest. Second, the captives deserved the punishment. Only the first of these reasons informed Moshe’s decision to introduce an approximation into this prophecy. The second reason was not relevant to Moshe’s decision. Therefore, Rashi does not include this second reason in his initial treatment of the issue.
 Rabbaynu Shlomo ben Yitzchak (Rashi), Commentary on Sefer Shemot 11:4.  Rabbaynu Shlomo ben Yitzchak (Rashi), Commentary on Sefer Shemot 11:4.