The Sefer Ha’hinuch, following the view of the Rambam, lists the prohibition against serving in the Bet Ha’mikdash with a physical blemish as two separate Biblical commands. One command forbids a Kohen from performing the service with a permanent blemish, and a different command forbids serving with a temporary blemish. An example of a permanent blemish, as the Sefer Ha’hinuch writes, is a broken arm or leg which does not completely heal, permanently compromising the limb’s functioning. An example of a temporary blemish is a pimple, boil or wart which heals. Of course, there is nothing intrinsically wrong with a Ba’al Mum (person with a physical blemish) an account of which he is disqualified from performing the Aboda (service in the Bet Ha’mikdash). In fact, fundamentally, a Ba’al Mum would likely be best suited for this role, because he feels humbled and subdued, and thus more readily subjugates himself to G-d’s authority. However, as the Sefer Ha’hinuch explains, the Torah disqualifies a Ba’al Mum for serving in the Bet Ha’mikdash because of the impression this would have on the people. Seeing a Kohen with a blemish serving might lower the people’s esteem for the service, because people are impacted by external appearances. As Rashi comments, when a government leader needs to send an emissary to another country, he will naturally choose somebody with an impressive appearance who makes a strong impression. By the same token, the Kohanim, who represent the people before G-d, should be unblemished, so that people regard the service with the respect and reverence it deserves. Although G-d most certainly does not need unblemished Kohanim, this is necessary because of the impression made upon the people. A Kohen who performs the Aboda with a blemish transgresses this prohibition, and the service is invalid. If he violates intentionally, he is liable to Malkut. The Rambam writes (Hilchot Bi’at Mikdash 6:11-12) that the Sanhedrin, which had its offices in the area of the Bet Ha’mikdash, would oversee a “vetting” process, checking each Kohen before he performs the Aboda. They would check his lineage, to ensure he is a valid Kohen, and they would inspect him to ensure he has no disqualifying physical defects. A Kohen who was discovered to be disqualified due to his lineage would be dressed in black garments and escorted out of the area of the Bet Ha’mikdash. Those whose status as Kohanim was confirmed were dressed in white garments and brought to do the service. If a Kohen was discovered to have a disqualifying blemish, he would be brought to a special room called the “Lishkat Ha’esim,” where the wood for the altar was stored. These blemished Kohanim, who could not perform the actual Aboda, were given the task of inspecting the wood for worms. These Kohanim received a share of the sacrificial food which was distributed among all the Kohanim who were on duty in the Bet Ha’mikdash. Even though they were not allowed to perform the Aboda, they were nevertheless allowed to partake of the sacrifices along with the other Kohanim. It should be noted that unlike the Rambam (and, following his lead, the Sefer Ha’hinuch), who listed two separate Biblical prohibitions for permanent and temporary blemishes, the Ramban listed just a single command, forbidding any Ba’al Mum from performing the Aboda. Although both the Rambam and Ramban came up with 613 Biblical commands (248 affirmative commands, and 365 prohibitions), they followed different methods of counting. For the Rambam, the prohibition against serving with a blemish is divided into two separate commands, whereas the Ramban understood that these are two components of a single Biblical command.