F. The reason the Jewish people needed to make signs by the plague of the firstborn:[1]

The difference between the plague of the firstborn and the previous plagues: There are a number of differences that we find between the last plague, the plague of the firstborn, and all the other previous plagues. By all the previous plagues, the Jewish people were naturally and automatically saved from any harm, as the plagues only attacked the Egyptians and did not spread to the Israelites. No mention is made that the Jewish people had to perform some matter in order to gain this protection. The protection was granted automatically, and was self-understood to be the case, as G-d did so for the sake of helping save the enslaved Jewish people from their Egyptian captors. However, by the last plague, the plague of the firstborn, the Jewish people were specifically instructed to smear blood on their doorposts in order so they would not be susceptible to the angel of death. They were instructed to circumcise themselves and to slaughter the Pesach lamb and then take from that blood and smear it on the doorposts. This matter is quite wondrous, as if the Jewish people were not required to perform any actions by the previous plagues in order to receive protection, then why should this be necessary by the final plague which was much more severe? Also, we need to understand the connection between the signs that they were requested to do and the protection that they gained through it.

The purpose of the plague of the firstborn: Unlike all the previous plagues, the purpose of the last plague, the plague of the firstborn, was to actually punish the Egyptians for their sinful behavior. It was no longer about teaching them a lesson of G-d’s powers and capabilities, but rather to actually punish them, and kill all their firstborn without survivors. Now, once we are dealing with the subject of punishment for sinful activity, the Jewish people were not all that righteous either. The attribute of judgment can make a claim stating that just as the Egyptians are sinners and guilty of idol worship, so too there are many Jews who are guilty of the same[2], and hence under which right should only the Egyptians be targeted. It would be very difficult for the angel of death to differentiate between the Egyptian and Jew when both are guilty of the same crime that he is prosecuting. It is for this reason that the Jewish people needed to make a sign to both give them a merit for which they will be protected and create a sign that will help the angel of death differentiate between Jew and Egyptian. We will now explore in greater detail the meaning of the blood which was smeared on the doorposts, and its significance in protecting the Jewish people.

The significance of the blood of the sacrificial lamb and the blood of the circumcision: The significance of the blood of the sacrificial lamb and the blood of the circumcision, which the Jewish people were instructed to smear on their doorposts, can be derived from the challenge of their fulfillment. In order for the Jewish people to merit being saved from the angel of death that spared no firstborn on the night of the 15th, they were required to perform a Mitzvah of complete Mesirus Nefesh. This Mitzvah of illogical performance, would then arouse the illogical within G-d and have their sins be ignored. By them doing a Mitzvah which puts their own life in danger simply for the sake of G-d, it aroused a desire above within G-d to ignore even the most severe of sins. The slaughtering of the Passover lamb involved literal Mesirus Nefesh, as the sheep was considered an Egyptian deity, and through slaughtering it in public they put their very lives in danger. The illogical and irrational behavior of the Jewish people in circumcising themselves and slaughtering the Passover lamb likewise aroused an irrational, above intellect, interaction from G-d that He desired not to exact punishment for their sins. Thus, we find that the sages[3] state that it was in the merit of the two bloods, the blood of the Passover lamb and the blood of the circumcision, that we left Egypt.

[1] Likkutei Sichos Vol. 3 Parshas Bo

[2] See Yalkut Reuveini Shemos 14:27; Zohar Chadash Parshas Yisro

[3] Pirkei Derebbe Eliezer 29; Mechilta Shemos 12:6