the Messiah will make a sin-offering FOR himself, not of himself, AND also for ALL the people of Israel:
Ezekiel 45:22(JPT) – And the prince shall make on that day for himself and for all the people of Israel a bull for a sin-offering.
The Messiah will make this sacrificial sin-offering on behalf of himself and his people
sin offering is a mitzvah
it has specific requirements
and one of those is that the one offering one for himself needs to have done something that requires it, otherwise not only is he doing the mitzvah in vain, he is actually committing a sin, namely, the killing of an animal for nothing – violating the mitzvah of tza’ar ba’alei chayim.