John Wesley on Numbers 6:5

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 outward beauty; 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 Num 6:9, partly that by the length of his hair he might be constantly minded of his vow; and partly that he might reserve his hair entirely for God, to whom it was to be offered. Holy - That is, wholly consecrated to God and his service, whereby he shews that inward holiness was the great thing which God required and valued in these, and consequently in other rites and ceremonies.