These prohibitions given to the people at large (compare the margin reference.) had a special fitness for the Hebrew priests. They were the instruments of the divine will for averting death, all their sacrifices were a type of the death of Christ, which swallowed up death in victory 1 Corinthians 15:54-57, and it would therefore have been unsuitable that they should have the same freedom as other people to become mourners.
Related Commentaries of Leviticus 21:5
Leviticus 21:5
5 They shall not make baldness upon their head, neither shall they shave off the corner of their beard, nor make any cuttings in their flesh.