The tenth and final plague which G‑d visited upon the Egyptians was the Plague of the Firstborn, which Moshe indicated would take place at midnight.1 To shield themselves from this plague, Jews were to sprinkle blood from the Paschal offering and from milah , circumcision, on their doorposts.

Why did Moshe indicate when this plague would take place? He didn’t do so for any of the other plagues. Also, why was it necessary for the Jewish people to seek protection from this final plague, though they didn’t have to take precautions against the previous nine?

The purpose of the last plague was not only to have the Egyptians become aware of G‑d’s might, but also to rain personal destruction upon them. At such a time, it was possible for the Attribute of Justice to declare: “How are they [the Jews] different from them [the Egyptians],” for there were Jews in Egypt who were mired in idolatry.2 It was thus conceivable that some of the Jewish people would also suffer dire consequences.

In order to remove any possible complaint about the Jewish people, G‑d brought the final plague at precisely midnight, so that it emanated from a level at which logic (and the complaint of the Attribute of Justice) had no standing.

The explanation is as follows: The first part of the night is symbolic of and related to severity, and thus, during this part of the night, it becomes increasingly dark. The second part of the night is symbolic of and related to kindness, for which reason the darkness lessens.

The moment of midnight unites the two opposites, kindness and severity, since, at that time, there descends an illumination of G‑dliness that wholly transcends the natural order. For only something entirely higher than two opposites can unite them.3

In other words, at the time of the final plague, there was a manifestation of the essential love that G‑d has for the Jewish people — a love that transcends all logic and reason. Because of this love, when the Attribute of Justice asks: “How are they different from them,” G‑d responds that, whatever their state, the Jewish people are His children. And the love of a father for his children cannot be affected by any logical complaint.

But this gives rise to the following question: Since G‑d’s love for the Jewish people was made manifest at the stroke of midnight, why was it necessary for them to mark their doorposts?

Since all Divine beneficences down below come about through the spiritual service of the Jewish people, even this transcendent degree of Divine love had to be drawn down through their service. For although this love is always whole and complete, in order for it to manifest itself below and be received in an inward manner, there had to be a degree of service consonant with that which was being revealed.

This is why the sign on the Jewish houses consisted of the blood of circumcision and of the Passover offering, as both indicate a level of service that transcends logic: The bond between a Jew and G‑d achieved through circumcision is above logic, as we see from the fact that the mitzvah takes place while a child is utterly incapable of understanding the deed.

Bringing the Paschal offering in Egypt was also bound up with self-sacrifice, and beyond logic, for the lambs used for the offering were worshipped by the Egyptians. Nevertheless, the Jewish people took the lambs, kept them for four days, and declared that they were going to sacrifice them to G‑d.

This manner of service above and beyond the level of understanding elicited a similar response from G‑d — the revelation of His limitless love for the Jewish people.

Thus, our Sages say4 that it was “in the merit of their faith [in the coming redemption] that our ancestors were redeemed from Egypt.”

For faith too transcends the bounds of logic.

Based on Likkutei Sichos, Vol. III, pp. 864-868