The Midrash explains that the nazir cannot cut his hair because a haircut beautifies a person and allowing hair to grow wild makes a person feel disheveled and downcast. Hashem said: “Since this person has accepted upon himself to become a nazir in order to avoid immorality, let him also grow his hair to prevent his evil inclination from becoming aroused and leaping upon him” (Bamidbar Rabbah 10:10). In other words, having a good appearance makes a person attractive and inflates his pride, which encourages immorality. Hashem advises the nazir to counteract this by going to the other extreme and letting his hair grow wild.
This does not mean that a nazir actually feels disheveled and downcast. The Torah calls a nazir’s hair “the crown of his God.” A nazir replaces the pride of his body with the true pride of subjugating his body to Hashem’s kingship, so he wears Hashem’s crown. Ibn Ezra remarks: “Know that all people are slaves to earthly desires. The only true king, who has a majestic crown on his head, is someone who is free from the subjugation of earthly desires.” The Kabbalists speak at length about the holiness of a nazir’s hair and the reason why Shimshon’s nazirite hair gave him Divine strength. Thus, by growing his hair, the nazir humbles his body but elevates his soul.
