Two-minute Torah: Nadav and Avihu died for your sins?

Dear Friends:
There are teachings in each religion that those of other religions
often find puzzling. In my experience, one of the Christian ideas that
Jews find to be odd or problematic is the teaching that Jesus died for
our sins. It seems pretty strange. Each of us is responsible for the
wrongs that we do. How can someone else's death atone for my sins?
This week's Parasha, Shemini, contains the story of the death of Nadav
and Avihu. They were the two oldest sons of Aaron. They went into the
Tabernacle to offer a sacrifice -- one which they had not been
commanded to make -- and were burned up. Moses says to his brother
Aaron: "I will show myself holy through those who are near to me, and
I will be glorified before all the people." And Aaron was silent.
Moses then says that he and his surviving sons are not to perform the
typical mourning rituals on behalf of Nadav and Avihu, "but your
brethren, the whole House of Israel, may bewail the burning which the
Lord has kindled."

Most commentators have assumed that the deaths of Nadav and Avihu were
a punishment, and have tried to figure out what the punishment was
for. Most focus on one of two ideas. Either the punishment was for
religious innovation -- we are supposed to do the rituals we are
commanded by God to do and not invent our own. Or for drunkenness --
while the text does not explicitly tell us they were drunk, the Torah
does tell us shortly after this story that Kohanim, priests, are not
allowed to drink alcohol prior to performing the sacrifices.

The Sefat Emet, a Chasidic commentator who lived from 1847 to 1905,
offers another possibility. Here is his comment on the story:

"Concerning the verse but your brethren, the whole house of Israel,
may bewail the burning which the LORD has kindled. It appears that
every man of Israel is obligated to weep for them, as it is written in
the Holy Zohar, Parashat Acharei. And the matter can be explained in
this way: they were completely righteous (tzaddikim g'morim). And our
sages have said that "in the place where a penitent (ba'al teshuvah)
stands, the wholly righteous cannot stand. This being the case, they
were punished on our behalf, therefore we have to weep for them. And
it is best not to go on about this matter."

What is the Sefat Emet saying about Nadav and Avihu? Were they sinners
or saints? Was their death punishment or vicarious atonement? And why
is it best not to go on about this matter?