What is the significance of taking the blood and placing it ... ?
Rashi: They performed Kabalas ha'Dam by taking the blood from the bowl (See Pasuk 22) ...
Where exactly did they place it?
Rashi: And they placed it on the inside of the doorposts and lintel. 1
Targum Yonasan: They placed it on the outside. 2
What is the "Mashkof"? Why is it called by that name?
Rashi: Mashkof is the lintel, so-called because (Shakof means to bang and) the door bangs against it. 1
Hashem told Moshe "Al ha'Mezuzos v'Al ha'Mashkof." When Moshe told Yisrael (verse 22), why did he say "Al ha'Mashkof v'Al Shtei ha'Mezuzos"?
Riva citing R. Yosef of Paris: Moshe deviated, lest people say that both are required only when one puts on the Mezuzos first, but if puts on the Mashkof first, this is enough, for in any case blood will spill onto the Mezuzos!
Moshav Zekenim (22) #1: The blood on each Mezuzah is like the letter Yud, and on the Mashkof is like Vov. In all, their Gematriya is 26, like Hashem's name, to scare away Mazikim. Moshe changed the order, for it is not proper for His name to be written in order amidst Tum'as Egypt. 1 3. Moshav Zekenim (22) #2: Hashem in His humility hinted that Yisrael are saved in the merit of Moshe and Aharon (the blood on the Mezuzos below) and Himself (the blood on the Mashkof above). Moshe deviated, for the merit of Hashem must be first.
Tosfos ha'Shalem (22:5): This is difficult. In any case His name is not written. There is merely a hint through the Gematriya!