The law stipulates that a Kohen is to remain TAHOR or pure at all times and is not to come in contact with the dead. The exception to this rule is that he may attend the funeral of a close relative although that would defile him and make him TAMME.
In today’s Sidra we learn the laws of a NAZIR or a Nazarite, that is, one who accepts upon himself the prohibition of drinking wine, cutting his hair and the prohibition of coming in contact with the dead. He too must not defile himself and is thus prohibited just as the Kohen is from coming near a dead person. There is a distinction, however. Unlike the Kohen, he must not even attend the funeral of his close relatives. Why the difference?
One explanation given is that this restriction was placed on the Kohen by the Torah and so the exception was made in the case of his immediate family. The NAZIR, on the other hand, was not prohibited but took upon himself an additional CHUMRA or stringent restriction not called for by the Torah. He should have considered the possibility that he may find himself in a situation where his restriction would be a true handicap.
One of the acts the Torah requires at the end of his term of being a NAZIR is for him to bring a sin-offering. (Num. 6,14) Our Chazal ask why a sin-offering? What is the sin he committed? They answer that a person who restricts what is permitted is performing a wrong act. One who prohibits what is permitted is considered a transgressor. (See Nedarim 10a)