The parsha starts off with the pasuk (19:2) "Speak to the entire assembly of Bnei Yisrael, and say to them 'be holy (kadosh) because I, Hashem their God, am holy.'" The Ramban on this pasuk says that the halacha of being kadosh is not just following the letter of the law, but one must go farther and remove himself/herself even from that which is permitted.
There is a basic idea in Judaism that is brought down in Mesilat Yersharim (Perek 13) "The bad separation... that is done by removing not only that which is not necessary but also removes what is required for living, is not a desire of Hashem's. In fact the talmud says, Taanit (22b) 'A man is not allowed to mortify himself.'"
We see from here what seems to be a clash. The Ramban says that the more one removes himself from the physical the better, but the Ramchal says that if one removes too much he has actually gone against Hashem's will.
The Ramchal himself answers the question. He says that "This is the true principle: Anything that a person does not require in this world it is good to separate from. But, anything that one requires, for whatever reason it may be, since it is required for him, if he separates from it- he is a sinner."
The pasuk seems to hint at this answer. The pasuk uses the phrase "to the entire assembly" according to some mefarshim that means that the way that Moshe taught it to the nation was by first teaching it to Aharon and his sons, then the zikainim, then the rest of the people. From here we see that the Mitzvah was given to the people on their level.
This is the same way one must decide how much hishtadlut he must do. If one completely believes that Hashem controls everything then technically speaking he should not have to work. But for someone who is not on that level, then hishtadlut would be required.
May we all be zoche to reach the highest level we can reach and become kadosh.