Bekhorot 43B

מאי איכא בין מומא לשאינו שוה בזרעו של אהרן? איכא משום אחולי עבודה: מומא מחיל עבודה, דכתיב: ״מום בו ולא יחלל״, שאינו שוה בזרעו של אהרן לא מחיל עבודה.

The Talmud asks: What difference is there between a priest disqualified from performing the Temple service due to a full-fledged blemish that disqualifies both people and animals, and a priest disqualified from performing the Temple service because he is not equal among the seed of Aaron? The Talmud responds: There is a difference between them with regard to profaning the Temple service. A priest with a full-fledged blemish who performs rites in the Temple profanes the service he has performed, as it is written: “He has a blemish; that he not profane My Sanctuaries” (Leviticus 21:23). A priest who is not equal among the seed of Aaron does not profane the service he performs.

מאי איכא בין שאינו שוה בזרעו של אהרן, ומשום מראית העין? איכא בינייהו עשה.

The Talmud further asks: What difference is there between a priest disqualified from performing the Temple service because he is not equal among the seed of Aaron, e.g., one whose head is pointed, and a priest disqualified from performing the Temple service due to the mere appearance of a blemish, such as one whose eyelashes have fallen out, as stated in the mishnayot further on in this chapter? The Talmud responds: There is a difference between them with regard to the violation of the prohibition, which is stated as a positive mitzva, i.e., that priests who are equal should serve in the Temple. A priest who is not equal among the seed of Aaron who performs the Temple service transgresses this prohibition. By contrast, a priest who is disqualified due to the appearance of a blemish is disqualified by rabbinic law, and he does not transgress a Torah prohibition by performing the Temple service.