When Moses informed Pharaoh about the tenth plague, the death of the firstborn, he said it would occur around midnight. Why did God give the time when the plague would occur, when He did not do so with the other plagues? What is the difference between this plague and the others? Another notable difference is that God commanded the Jewish people to make a mark on their doorposts so they would not be affected by the plague. Since the destroyer was given permission to destroy, there were no distinctions between the righteous and the wicked, so a mark was necessary to distinguish between the Jewish people and the Egyptians.
However, apparently, in previous plagues, the destroyer was also "given permission," and yet the Jews were not affected. Why, specifically, did the plague of the firstborn need to have a sign?
The difference between the tenth plague and the previous ones is that in the earlier plagues, the means of "giving permission to the destroyer" was limited. Even those plagues that affected both the Egyptians' possessions and their lives, like the plague of wild beasts, were limited in their methods of destruction, restricted to the type of destruction that plague could cause. limited. The plague of the death of the firstborn consisted of a death unlimited, Since there was no specific way in which this plague acted, a sign was needed to differentiate Jews from Egyptians.
A deeper difference: the objective major The purpose of the plagues was not to punish the Egyptians, but, as the Torah itself states, "that they may know that I am God." This is why the plagues did not affect the people of Israel, since they already recognized God as Master of the universe. However, the final plague was intended to kill the firstborn, not "that they may know," since those affected by this plague died! Therefore, it was necessary to warn against the possibility that the Divine attribute of severity and judgment might not differentiate between Jews and Egyptians, since, as our sages recount, the Jewish people were steeped in the impurity of Egypt, to the point of idolatry. To highlight the difference, a sign was needed.
However, the question remains: If the level of the Jewish people was so low that it was possible that "the destroyer" could affect them as well, how would a sign help to save them?.
To understand the answer, we must understand the source of the plague of the death of the firstborn. Our sages say that this plague was carried out by "The Holy One, blessed be He," who is above His own attribute of judgment. In the essence of God, there is no place for judgments and sentences against the Jewish people.
From this explanation, we will understand why this plague had to occur at midnight. The wisdom of Kabbalah explains that the night is divided into two parts: the first part is governed by the Divine attribute of severity (and judgment), since we see that the darkness deepens as the night progresses, and the second half is governed by the Divine attribute of kindness, since the light intensifies with the arrival of day. Midnight indicates the moment when these two attributes, severity (darkness) and kindness (light), unite. The union of two opposites is only possible with the revelation of a level that is above both: "The Holy One, blessed be He.".
This means that the plague of the firstborn revealed the essential love between God and the Jewish people, a love that is independent of the people's behavior. It is like the love between a father and a son, which cannot be diminished by any cause and is fundamental.
That is why Moses had to tell Pharaoh the time this plague would occur, to indicate the spiritual level from which it originated, so that he and his sages would not think that a plague where "permission was given to the destroyer" would affect the Jewish and Egyptian people equally. This plague would occur "at midnight.".
With all this in mind, it was necessary for the Israelite people to place a sign on their doorposts to distinguish themselves. This contains a particular lesson. Every divine blessing must be brought into the physical world through action. Even though "The Holy One, blessed be He" was revealing His essential love for the Jewish people, in order to materialize that love in their salvation from the plague and subsequent redemption from Egypt, there had to be an action on the part of the Jewish people through which the divine revelation could be channeled.
Similarly, today, just as we left Egypt, we can leave this prolonged exile, and it depends solely on our actions in Torah and Mitzvot today.
Extracted from Likutei Sijot, Vol. 3, p. 864