In Chapter 21 Pasuk 18 the Chumash states that a Kohen with a blemish may not perform the service in the Bait Hamikdash. To explain this prohibition, Rashi quotes from the book of Malachi (1:8), which says that a king would not accept an animal with a blemish. If bringing an animal with a blemish shows a lack of respect, we can assume the same principle would apply to the Kohanim, the servants of the King.
Rambam views the requirement that the Kohen not be blemished to be based on the nature of public opinion: that a man is not judged by who he is, but by his appearance. Therefore, it is necessary for the Kohanim to be unblemished so that the Mikdash would remain honored and revered by all. The Rambam points out that this prohibition applies only to Kohanim and not the Leviim since the Leviim did not offer sacrifices and were not considered agents in asking for forgiveness.
The Ramban differs from the rationalist view of the Rambam. He says that bodily blemishes render the Kohen unfit for work in the Mikdash because these physical blemishes are a reflection of spiritual defects that he might have.
Rabbi Shimon Bar Yochai suggests a very different approach. The laws pertaining to blemishes fit into the general framework of the origin of evil. The forces of evil exist in nature to play a role in the harmony of Creation. However, the power of the forces of evil is restricted and limited to the superficial aspects of life, to the external appearance, not to the core of the person.
This Parsha is teaching us that evil affects the body, not the soul. The Kohen, who is the epitome of purity and holiness, is not protected from evil and can therefore have blemishes. However, his soul is not affected by the evil. The Torah tells us this by saying that even though a Kohen with a blemish cannot approach the altar, he can eat “the food of his God, from the most holy and from the holy” (Pasuk 22). By saying that a Kohen with a blemish can eat from a Korban, the Torah confirms that his blemish is merely external, and has no affect on his soul.
Rabbi Shimon Bar Yochai equates this to the moon. Because the moon disappears each month, it seems to have a blemish in comparison with the sun. The moon shows us that there is evil in this world, but this evil does not affect the soul, since each month the moon recovers its full powers again. The prophet Yishayahu (30:26) speaks of the day when “the light of the moon will equal the light of the sun.” When this happens, the evil of this world that afflicts blemishes on Hashem’s creatures will also disappear.