Rabbi Shimon tells us why God required the sign of blood to be placed outside the entrance so that He would pass over Yisrael's houses when He killed the Egyptians. He says that idol worshipping is the only thing which is punished without a person having had to commit an action of some kind. The blood placed on the three places of the lintel and side posts corresponds to the three columns. There is some discussion of the color of the columns and the color of blood, and of the two bloods of Passover and Circumcision that correspond to Mercy and Judgment. At the same time that the Egyptians were being killed, the children of Yisrael were being healed from their circumcision. We are told that the entrance, in "And Hashem will pass over on the entrance," is the opening to draw the spirit and the body, which opening is only freed upon circumcision. Rabbi Aba says that when "pass through" is written, as in "And Hashem will pass through to smite Egypt," it always means that God passed down through the emanations of the Sfirot to perform either Judgment or Mercy.