The Torah, at Lev. 19:2, teaches "You shall be holy for I, Hashem your G-d, am holy." What is holiness in this context? Is it an achieveable goal, or must we observe the commandments perfectly? If the latter, does "perfect" mean 100 percent observance without mistakes, or does it indicate one did not sin intentionally? Also is "holiness" the same as "righteousness"? How does the meaning of these two words differ?
Leviticus 19:2 is part of Parshah Kedoshim, and so this is a common question brought up in dvar torahs. Here is a prompt based on the teachings of Rabbi Nachman of Breslov:
Everybody knows that being holy means praying a lot, learning a lot of Torah and being scrupulous in ritual observance.
That also. In fact, this is the easier aspect of holiness. But there is another aspect of holiness, one that's harder to attain and maintain, the aspect which involves human interaction: being generous, helpful, offering honest advice; paying employees on time; not lying, cheating or stealing; giving others the benefit of the doubt; no gossiping, taking revenge or bearing grudges.
In other words, being an honest, decent human being, even when you have to deal with people are annoying, wearying, dishonest or disingenuous. However, for the holiness to kick in, you've got to follow these common-sense rules for getting along with others for the right reason. The right reason is not because it's the ethical way to behave or the ethical thing to do. The right reason is because God said so. They are mitzvot.
Rabbi Nachman (or what is based off of Rabbi Nachman) is not alone in his third requirement, to accept these easy "common-sense rules for getting along with others for the right reason." Rambam also reflects this too in Laws of Kings and their Wars 8:11:
But if he [a Ben Noach] does them [fulfill the Noachide laws] because of an intellectual decision, then he is not a Ger Toshav [resident alien], and is not of the Chasidei Umos HaOlam [pious ones of the nations], he is [only] one of their wise men (of the nations of the world).
Rambam here distinguishes between a pious one among the nations and a wiseman by how one comes about accepting the Noachide laws. If one comes about accepting them through compelling common-sense reason and logic, then he is only a wiseman as opposed to a pious man. This same line of reasoning is used in Rabbi Nachman's last requirement to achieve holiness.
I hope this helps. If you want, just search for other dvar torahs on Parshah Kedoshim with a keyword, "holiness," and you should get plenty of results.