ואחר ישתה הנזיר יין, "And after the sacrifice is brought the nazir may drink wine." The Alshich Hakodesh questions the last words of the Pasuk: why does it say, "Then the Nazir may drink wine." It should say, "Then he is allowed to drink wine," since he is no longer a Nazir.
The Alshich answers: if an individual can make a vow to hold back from benefiting from certain material pleasures, and if he can make a vow to bring himself closer to Hashem, then has lived on a higher level of life than the rest of the world.
Although this period of Nizirut may end at an appointed time, the elevated level of this individual does not end with the conclusion of the period of Nizirut. He must try to retain the high position that he has set for himself. Although the Nizirut is over and he is allowed to drink wine he should do so with the same spiritual elevation that he had before.
It is very similar with teachers of Torah: Once they reach levels of understanding of what it means to work for the Torah, they can never give up. They must not sit back and step aside to allow someone to take over, although they can step aside to help others become interested in the same line of work, and allow others to work for Torah. Once an individual consecrates himself to God's work, he must always continue to work for God.