“When a person makes a vow to G-d” (30:3)
At first glance, the advice of the Jerusalem Talmud, that one should avoid making vows, appears to contradict the Mishnah’s teaching that vows are a valuable tool for a person to restrain himself from physical indulgence.
In truth, however, there is no contradiction, since these two texts are addressing two different types of people. The Mishnah addresses a person who cannot restrain himself from excessive physical indulgence which interferes with his observance of Torah. Thus for him the only solution is to make a vow of abstinence. The Jerusalem Talmud, however, speaks of a person who is able to utilize physical pleasures for holy purposes, and for such a person it would be inadvisable to abstain from these physical things, since the purpose of creation is to sanctify the physical world, so that it becomes a “home” for God below.
Based on the above we can also appreciate why an “expert” may release a person from his vows (see Rashi to v. 2). For, at first glance this is difficult to understand: Surely the purpose of a Jewish sage is to guide a person to a more spiritual life; so if a person has vowed to abstain from something physical should he not be encouraged to do so by the sage, and not be released from his vow? In truth, however, one who is at the highest level of Godly service must involve himself with the physical world to sanctify it. And it is to this goal that the sage attempts to lift the person, rendering the vow unnecessary.
(Likutei Sichos vol. 13, pp. 107-8; Sichas Shabbos Parshas Matos-Masei 5733)