Paterius

Hairs of the flesh mean whatever human corruption is left. Hairs of the flesh are the thoughts of the old life, which we so expel from our minds that no grief at their loss fatigues us. Levite means "one taken up." So all Levites should shave the hairs of the flesh. For he who is taken up into divine service should appear before the eyes of God cleansed of all carnal thoughts. His mind should not bring forth illicit thoughts and deform the beautiful shape of his soul with unruly hair. …

Exposition of the Old and New Testament, Numbers 3