Parshas Bechukosai does not begin, as so many other parshiyos do, with "Vayidaber Hashem el Moshe leimor," or "Vayomer Hashem." Why is that? Because, explains the Ishbitzer, the ideal of "Bechukosai teileichu" is not one which can be commanded or achieved through effort. One must be zoche to it. A person lives in a perpetual state of "im b'chukosai," existential doubt as to where he really stands viz a viz G-d's expectations. When you read social commentary, isn't it amazing about how certain people are in their positions? I don't think it's just a facade for writing or debating; I think it's how they really feel. We've lost sight of that little word, "im."
Why the word "bechokosai" -- We aren't dealing with esoteric halachos here whose reason is unknown? The Midrash explains the derivation of the word chok as used here:
חקים שבהם חקקתי את השמים והארץ
The moral order of Torah, the idea of bracha for doing good and tochacha for failing to do good, is not superimposed on top of the bri'ah, but is inherent within it. The rules of Torah are engraved into the fabric of the natural world (see Nefesh haChaim). We once explained that this is the meaning of the Midrash that Hashem created the sea on the condition that it splits when Bnei Yisrael needed it to.
The Midrash continues that unlike a King who commands others but lives above the law, Hashem himself fulfills the mitzvos even before we do:
גוזר גזירה הוא מקיימה תחלה
If mitzvos existed only for some utilitarian purpose -- for a healthy lifestyle, to have an ordered society, etc. -- it would make no sense for G-d himself to observe them. G-d can not be healthy or ill; G-d has no society he needs to live in or perfect. Why does G-d do mitzvos? We know that G-d sustains the world, he is mechadesh... ma'aseh braishis every moment. Since mitzvos are part of the world's natural order, they are kept even by G-d himself. It follows that a person who keeps mitzvos fulfill this same role of sustaining the world (see Netziv on the parsha's opening).