Numbers 6:5 - Matthew Poole's English Annotations on the Holy Bible

No razor, nor scissors, or other instrument to cut off any part of his hair. This was appointed, partly, as a sign of his mortification to worldly delights, and vain affectation of outward beauty, which is promoted by the polling or cutting off the hair; partly, as a testimony of that purity which hereby he professed, because the cutting off the hair was a sign of uncleanness, as appears from Numbers 6:9, and Leviticus 14:8,9; partly, that by the notorious length of his hair he might be constantly minded of his vow, and the exquisite holiness it required, and that others might thereby be admonished and stirred up to the imitation of his holy example; and partly, that he might reserve his hair entirely for God, to whom it was to be offered, Numbers 6:18. He shall be holy, i.e. wholly consecrated to God and his service, whereby lie shows that inward and substantial holiness was the great thing which God required and valued in these, and consequently in other rites and ceremonies.