The following section of the Zohar explains the commandments the Israelites were given leading up to the final tenth plague, that of the death of the Egyptian firstborn males. The Jewish men were told to circumcise themselves and to sacrifice the Paschal lamb and smear some of the blood on their doorposts and lintels above the door.

"G‑d will pass through and strike Egypt. When He sees the blood over the door and on the two doorposts, G‑d will pass over that entrance and He will not permit the destructive forces to enter your homes to strike…" (Ex. 12:23)

Are we to understand that a sign was necessary for G‑d?

We have learned that Rabbi Yose said: This verse presents a problem. Could it be that only when He saw the blood would He skip over [that home]? Are we to understand that a sign was necessary [for G‑d]?

Surely G‑d would know which one was an Israelite house and which was an Egyptian house without the blood smeared on the doorposts!

And if you answer that this was necessary in terms of the commandment of the blood, then why [was the blood smeared] on the outside [rather than on the inside of the house]?

Since the Israelites in their exile had already sunk to the forty-ninth gate of spiritual impurity, (See Ohr Hachaim, Shemot 3:7) there was very little difference between them and the Egyptians. Accordingly, G‑d gave them two commandments, the blood of the Paschal lamb and the blood of circumcision, (Shemot Rabba 17:3) as the verse states: "I passed over you and saw you wallowing in your bloods, and I said to you, 'In your blood you shall live'; and I said to you, 'In your blood you shall live.'" (Ezekiel 16:6) Note that the word "blood" in this verse is in the plural, alluding to the blood of the Paschal lamb and the blood of circumcision, and therefore the verse continues, stating twice, "in your blood you shall live". They saved their lives by fulfilling these two commandments.

He reveals the deepest secrets and mysteries….

Whether the blood was smeared on the doorposts and the lintel on the outside of the house or the inside of the house is a subject of disagreement among the Sages of the Midrash. (Mechilta, Bo 6) This may also be connected with the disagreement whether the statement in the Pesach Haggadah should read: "A person is obligated to view himself as if he just left Egypt" (Pesachim 116b) or "A person is obligated to show himself as if he just left Egypt". (Rambam, Yad Chametz u'Matzah 7:6) According to the former opinion, the blood was on the inside ("view himself"), but according to the latter opinion, it was on the outside ("show himself"). However, it seems that the Zohar here follows the view that the blood was smeared on the outside of the entrances.

Furthermore, why [were they commanded to smear the blood] in three places of the entrance?

They shall take of the blood and place it on the two doorposts and on the lintel of the houses…" (Ex. 12:7. See also 12:22, 23)

It is written, "He reveals the deepest secrets [and mysteries. He knows what is in the darkness, and light dwells with Him]" (Daniel 2:22). What then is the reason that He wanted the blood to be visible upon the lintel and the doorposts?

...Divine Providence is not manifested Above until a deed is done below….

However, it is written: G‑d will see and be provoked [by their transgressions](Deut. 32:19), and G‑d saw that the wickedness of man was great upon the earth (Gen. 6:5) [and decided to erase man from the face of the earth. From these verses] we learn that Divine Providence is not manifested Above until a deed is done below. But once a deed is done, the [corresponding] divine providence is aroused. Accordingly, everything, whether good or bad, depends on action.

Since everything depends on the deeds of those below, had they acted in secret, the divine intervention would have also been manifested in hidden ways. Now we can understand why the blood had to be placed on the outside of the houses according to this opinion in the Zohar: in order to fulfill the commandment in an open and revealed manner, so that the divine intervention would also be manifest in a revealed way.

[Translation and commentary by Moshe Miller from Zohar II:35b; based on R. Chaim Vital and Matok Midevash]