Many korbanot (offerings) have to be accompanied by nesachim (libations), a mincha (meal offering), and wine. We’ll talk about which korbanot require these nesachim. The Mishnah says: All communal and individual korbanot require you to bring nesachim with them.
The exceptions to the rule are the Bechor (firstborn), which is an animal tithe—you bring every tenth animal to the Beit HaMikdash—the korban Pesach (Passover offering), and all the korbanot that are chatat (sin offering) or asham (guilt offering). But there is an exception to that rule when it comes to chatat or asham: We say you do bring nesachim, but unlike the other korbanot of chatat and asham, the chatat and asham of a metzorah require nesachim.
The Gemara brings down the reason for the distinction between the two. When it comes to a standard chatat and asham, they’re coming to atone for sin. Therefore, it’s not befitting that we bring nesachim with them to beautify them. But the metzorah, on the other hand, already received his kapara (atonement) through the pain and suffering of the tzaraat (skin affliction) that he has. So the korbanot that he’s bringing are not for kapara, but for the purification process that permits him to eat sacred foods afterward. Therefore, when it comes to the person with tzaraat, he brings nesachim as well to help him beautify the mitzvah (commandment).