This week's portion is called Naso, which means "count." God continues the commandment to Moses to count the Levites. Among the topics discussed in this parashah is the law of the Nazirite. This refers to a person who makes a vow, for at least the next thirty days, not to cut their hair, drink wine or its derivatives, or defile themselves with the ritual impurity of a dead body.
Once the period of vows was over, the Torah commanded him to offer sacrifices in the Temple so that the Nazirite could cut his hair, drink wine, and become ritually impure if he so desired. Among the sacrifices to be brought was one of the Chatat type, which was brought, on other occasions, for having committed an unintentional sin.
Now, our sages ask, what sin did the Nazirite commit to warrant bringing a Chatat? On the contrary, the Torah considers him a holy person! To which they reply that his sin was abstaining from wine; in other words, if the Torah already forbade him from certain things, he shouldn't have forbade himself even more.
This principle appears to contradict another concept: "sanctify yourself in that which the Torah permits." The Torah states in Leviticus 19:2: "[...] be holy, for I am holy." From this, our sages learned that a person should not only abstain from what the Torah prohibits, such as non-kosher meat or theft, etc., but should also sanctify themselves—that is, abstain and exercise self-control—even when it concerns something the Torah permits (see Nachmanides' commentary on the cited verse). Whether this is a biblical or rabbinic commandment is a matter of debate. According to those who consider it a rabbinic commandment, we could understand that while the Torah frowns upon prohibiting oneself, our sages, knowing human nature and observing the progressive decline in people's spiritual level, recommended and even commanded abstinence from what is permitted. But according to those opinions that claim it is a biblical mandate, it seems to contradict the Nazirite's idea. (This question is even more compelling according to the wisdom of Kabbalah, which frequently speaks of itkafia—subjugation—and ithapja—transformation of the evil inclination.).
One possible answer would be that the motivation in each case is different, which is why one case is considered "sinful" and the other is not. In the case of the Nazirite, his vow and behavior are evident to everyone: he lets his hair grow long, he doesn't participate in "parties" by drinking wine, etc., in which case everyone recognizes his holiness. This could lead us to say that the motivation behind his behavior is to be seen as holy by others, or, in other words, his goal is not to serve God, but himself.
On the other hand, in the case of someone who sanctifies himself in what is permitted to him, his motivation is purely and exclusively to serve God, to offer himself to God, and we see this from the fact that he (or she) is the only one who knows why he does not eat such and such a morsel, or why he does not say such and such a word.
That is why the Torah calls the Nazirite, whose motivation is misguided and selfish, holy, because that is ultimately what is seen in the world of action, but it commands him to bring a sacrifice at the end of his vow because of the negative nature of his motivation. Whereas in the other case, the Torah also calls him holy, and even more so, it sanctifies him with Divine holiness itself.
From this, we can draw a basic lesson for human relations: if your relationship with your neighbor is for your own benefit (that is, a selfish relationship), good things may come of it (just as the Nazirite is indeed called a saint), but it is still, at least subtly, a sin—selfish, egocentric, etc. But if your relationship with your neighbor is for the benefit of your neighbor, then God resides there.