There is a famous question regarding the events that transpired on the night of the plague of the firstborn in Egypt.
On the one hand, Hashem tells the Jews that they should prepare the korban Pesach and daub its blood on their doorposts. Further, they are instructed to remain behind their blood-marked doors and not venture outside during the night. This is a protective measure, for in seeing this, "… G-d will pass over your doorway and not allow the destroying angel into your houses to kill." [Shemos 12:23]
On the other hand, though, is the assertion that Hashem himself is the one who will be performing makkas bechoros, as He says, "And I will pass through Egypt on that night and I will smite every first born …" [Shemos 12:12]
So what destroying angel is Hashem protecting us from ?
The Vilna Gaon answers the question by pointing out that while G-d himself is performing the smiting of the Egyptians, there may be one or two Jews who have reached the end of their allotted time on this earth and are up for collection by the angel of death. If they were to die, the heavenly retribution against Egypt would be incomplete since they could legitimately point out that Jews died that night also. (It can be compared to a scorecard. Even though 236,986 to 2 is still an overwhelming victory – it's not that same as a shutout). It is to prevent this intrusion by the malach hamavess, and its unwelcome inference, that the blood is to be daubed on the doorposts.
The implications of this idea are awesome and staggering. An entire nation (estimated at 2-3 million people) performed a complex ritual and remained closeted in their houses all night to save the lives of one or two Jews! Surely, this display of profound unity is one of the merits that the fledgling nation managed to come up with to deserve Hashem's redemption.
And us? What would we do for the 'achdus' of our people, or for 'kavod shamayim'? And have we done it lately?