In the course of teaching Moses the laws of holiness, G‑d promised that it is indeed possible for people to hold themselves to these standards of behavior.
Help in Becoming Holy
וְהִתְקַדִּשְׁתֶּם וִהְיִיתֶם קְדֹשִׁים וגו': (ויקרא כ:ז)
[G‑d instructed Moses to tell the people,] “You must sanctify yourselves and be holy.” Leviticus 20:7

The Talmudic sages assure us that when we sanctify ourselves even in some small way, G‑d helps us become holy in a great way. When we resist the urge to indulge in some material pleasure, we generate an increase of holiness and of positive spiritual energy, which then descends and rests upon us.

This verse, then, can be interpreted as follows: “Sanctify yourself,” i.e., act in some holy way, even if such behavior seems to be beyond your present spiritual level, and you will “be holy” – ultimately you will attain that level of holiness, on account of the great holy energy that you have generated, which will then descend upon you.1