Jamieson, Fausset and Brown on Leviticus 21:16-24

16-24. Whosoever he be ... hath any blemish, let him not approach to offer the bread of his God--As visible things exert a strong influence on the minds of men, any physical infirmity or malformation of body in the ministers of religion, which disturbs the associations or excites ridicule, tends to detract from the weight and authority of the sacred office. Priests laboring under any personal defect were not allowed to officiate in the public service; they might be employed in some inferior duties about the sanctuary but could not perform any sacred office. In all these regulations for preserving the unsullied purity of the sacred character and office, there was a typical reference to the priesthood of Christ (He 7:26).