The Multi-faceted Super-Mitzva
And G-d spoke to Moshe saying: Speak to the entire community of Bnei Yisrael and say to them: K'DOSHIM TIHYU! Be Holy! - but the Torah doesn't stop there - because holy am I, HaShem your G-d.
Definitely sounds like a command. It is. But neither Rambam nor the Sefer HaChinuch count it as a mitzva among the Torah's 613, among the Taryag. This can be understood by seeing commands like K'doshim tihyu as super- mitzvot, whose scope is inclusive of many or all of the mitzvot in the Torah. Think of K'doshim tihyu as a VAT, valued added tax - or, to be cute, a VAM, value added mitzva which applies to every mitzva we have.
The term is quite appropriate, because in doing mitzvot with the proper attitude, with an enthusiasm which shows a love of Torah and Mitzvot, one does indeed add value to the mitzvot he performs. And to the prohibitions he avoids.
So too does going beyond the "call of duty", LIFNIM MISHURAT HADIN. When a person does more - goes further - than the halacha requires him to go, this too adds value to the person's performance of mitzvot. This is one of the facets of the super-mitzva of K'DOSHIM TIHYU.
It's not Shabbesdik! This is a concept that many of us grew up with. There was no specific statement in Shulchan Aruch to point to and say, this is why we should not do such- and-such. But there was a feeling that certain behavior, certain acts, shouldn't be done on Shabbat. Some Jews scoff at this idea. Sad. Because they are missing something. What are they missing? Is it allowed or is it forbidden? Not enough to ask just that. One has to ask if it is in the spirit of Shabbat to do it. That's what Shabbesdik means and that is part of K'DOSHIM TIHYU.
We are not talking here about Chumra for the sake of Chumra. We are talking about a sense of right and wrong beyond the letter of the law. We are talking about whole generations and/or whole communities that pass on a legacy of what fits the great challenge to be holy - as G-d is holy!
Don't make your davening like a burden, but rather like a heartfelt petition to G-d for mercy. That's a major aspect of the mitzva to daven. But that is also a facet of the super- mitzva of K'doshim Tihyu.
Shabbat can be strictly kept. Or it can be strictly kept and be a beautiful, spiritual experience. The latter is part of K'doshim Tihyu. Etc. Etc. Etc.