What is the significance of the Nazir not cutting his hair? We can understand that the Nazir’s abstaining from cutting his hair is to shun vanity, as is described later on in the mesechta 9b. 

The Rama in Toras Haolah (III:71) explains further that the Nazir is required to abstain from three aspects: He must not drink wine, he must not become impure and he must not cut his hair. Each of these abstentions relate to a different kind of hedonistic behavior. For indulgence in food and drink, he forgoes wine. For indulgence in material possessions he dulls his beauty by not barbering, thus reducing his arrogance and appearance of status. And for indulgence in sexuality, he stays away from impurity.

However, there is an interesting anomaly. If a Nazir becomes impure by touching or by being in the same room as a corpse he must start his counting all over again (see Bamidbar 6:9.) Yet, if he chose to drink wine or to cut his hair, though he has violated his oath, he does not have to restart the count. Why?

The Rama (ibid) explains that a person chooses to cut his hair or drink, it does not happen usually by accident. However, the usual manner that a person becomes exposed to a corpse is due to an sudden accidental death, as is actually described in Bamidbar 6:9:

וְכִֽי־יָמ֨וּת מֵ֤ת עָלָיו֙ בְּפֶ֣תַע פִּתְאֹ֔ם וְטִמֵּ֖א רֹ֣אשׁ נִזְר֑וֹ וְגִלַּ֤ח רֹאשׁוֹ֙ בְּי֣וֹם טׇהֳרָת֔וֹ בַּיּ֥וֹם הַשְּׁבִיעִ֖י יְגַלְּחֶֽנּוּ׃

If someone dies suddenly nearby, defiling the consecrated hair, the [nazirite] shall shave the head at the time of becoming pure, shaving it on the seventh day.

Thus, unlike drinking or shaving, which generally fall under behavior that is human choice and not divinely decreed, a death and resultant impurity is a divine message to the Nazir. He is being told that his abstentions have NOT been accepted. Whatever he was trying to accomplish was not sufficient so he must start his counting all over again.

It is a fascinating Rama, because the implication is that though we believe God’s Providence is over all actions, it seems that we attribute more divine significance and meaning to actions that we have less control over and are less in the realm of human choice.