7. Come and behold: on the night that the Holy One, blessed be He, wanted to slaughter all these firstborn, as we have learned, the singers came to sing for Him when night fell. THE HOLY ONE, BLESSED BE HE, told them that the time was not opportune TO SING ANY SONG, since the inhabitants of the earth were singing another song. At midnight, the north wind was stirring and the Holy One, blessed be He, was wreaking vengeance FOR YISRAEL. Yisrael were singing their song with loud voices and, at that moment, He made them free from everyone. The supernal angels and all the HIGHEST camps together were listening to the voices of Yisrael after they were circumcised, and marked their houses with that blood and the blood of the Paschal lamb with three marks, "upon the lintel, and on the two side posts" (Shemot 12:23).
8. What is the reason THAT THEY MARKED THE BLOOD OVER THE DOOR LINTEL AND THE TWO SIDE POSTS? It has already been explained. It is because it is a holy mark, and the Angel of Destruction had mercy upon Yisrael when he saw this blood that was marked on the opening. This is what is written: "Hashem will pass over the door..." (Ibid.). We must look closely here. If the Holy One, blessed be He, and no other messenger came and slew in the land of Egypt, what is the purpose of this mark over the door opening, since all is revealed to Him? In addition, what is the meaning of: "and will not allow the Destroyer" (Ibid.), WHICH MEANS IT WAS A MESSENGER? It should have said, 'and will not destroy.'
9. It most certainly is so, as it is written: "And Hashem smote all the firstborn" (Ibid. 29). "And Hashem" INDICATES Him, ZEIR ANPIN, and His courthouse, MALCHUT. That courthouse is present here. THEREFORE, IT SAYS, "THE DESTROYER." It is always imperative to show a deed BELOW in order TO AWAKEN A CORRESPONDING ONE ABOVE to be saved. BECAUSE OF THAT, IT WAS NECESSARY TO PLACE THE BLOOD OVER THE DOOR LINTEL AND THE TWO SIDE POSTS, TO AROUSE MERCY FOR THEM ABOVE. Similar to that are THE OFFERINGS on the altar; this is in order that the Destroyer shall not come there.