Why Physical Imperfections Exclude a Kohen from Service: Exploring an Ancient Perspective
In Jewish thought, a physical imperfection doesn't diminish one's spiritual value. Yet, a Kohen with a blemish is excluded from temple service because, in representative roles, external appearance holds significance.

In the section of Emor, it states: "Speak to Aaron, saying, any of your future descendants who has a defect shall not approach to present the food of his God."
Today, there is a strong effort to ensure equal treatment for those with disabilities, and everywhere is required to be accessible. Excluding someone from a role due to a disability is viewed as discrimination.
Among ancient societies, there were signs that disabilities were seen as a curse, as someone unworthy. In Babylon, for example, a person with a disability couldn't be a prophet. Even the Qumran sect in the Judean Desert during the Second Temple period didn't accept those with disabilities, viewing them as cursed and unworthy of purification and elevation.
However, the Torah has no mention of such an approach. On the contrary. Isaac, our ancestor, whose sight diminished, still had prophecy and Divine presence with him; Ahijah the Shilonite, whose eyes were dimmed due to age, possibly with cataracts, couldn't see but was spiritually perceptive; Jacob, our ancestor, who limped, had divine revelations; Moses, our great prophet, had a speech impediment (though not considered a physical defect according to Jewish law, as he served during the dedication days, unless that was a temporary directive).
An interesting idea was proposed regarding Huldah the prophetess, suggesting she might have been blind. There is evidence in the story of finding the Book of the Law by Hilkiah, where Josiah sends priests to Huldah to inquire about the book, but does not accompany them with the book itself. Perhaps because she was blind, it would serve no purpose to show her the book. She was stationed permanently "sitting in the Second Quarter,” likely referring to the Huldah Gates in the southern area of the Temple Mount, where she may have been buried, thus the gates carry her name (see Avot of Rabbi Natan 1:35).
It is clear, therefore, that within Judaism, someone with a defect is not considered spiritually lesser. However, a Kohen in service is invalidated if blemished because, in a representative role, the honor of the role is tied to the external appearance. Just as the outer beauty of the Temple is important, despite holiness having no inherent connection to beauty, so too its servants must be splendid.
The principle is: when it comes to matters involving everyone, such as work, wisdom, or spirituality, there's no difference between someone with a physical defect and anyone else. But for matters reserved for the few who are sent to represent, it would be disrespectful to send someone limited in a representative capacity.
Maimonides, in his Guide for the Perplexed (3:45), adds that there's also the impact of the representative's form on the public: "For a person isn't honored among the public for their true form, but for their complete limbs and beautiful clothes, and the goal is for this house and its servants to be revered by all."
He notes, if a Kohen with a defect serves in the Temple, it could lead people to disrespect the place. Just as if the Temple weren't built with dignity and beauty, it would harm the respect for the place, so too its servants, who serve Hashem, must make an impression on those who visit the Temple.
The book "Sefer HaChinuch" (mitzvah 275) offers another point: "It is possible that the perfection of form hints at matters through which one's thoughts purify and elevate their soul. Therefore, it's unfitting for there to be any change in form from any of its forms, lest the distracting thoughts caused by the change lead one's mind astray from the goal."
According to him, any defect diverts attention. As the sages said, a Kohen with painted hands shouldn't raise his hands for blessing, for all will look at his hands and the paint. So too, someone not like everyone else would disturb the intention and purity.
Yet, it's clear that the mere existence of a defect wasn't seen as proving something bad or negative.