[Avodah] The Main Idea of Judaism

[David Riceman]

The Rambam says that malchus shamayim is "ha'ikkar hagadol shehakol 
talui bo", which one can plausibly render as "the main idea of Judaism", 
but he also says that God wants people to have free will.

So one can certainly construe the question as what does "malchus 
shamayim" mean.  Like almost all rishonim, the Rambam did not think that 
God has determined every detail of the future; he believed that the laws 
of nature left room for randomness.  My take on the Rambam is that he 
thought it meant the world has a unifying order, unlike, say, the 
Zoroastrians or Hegel who thought that the world consists of struggle 
between contradictory themes.

Most people here seem to construe the question as normative: what does 
Judaism expect of people? I think the Rambam would disagree with all of 
the suggestions people have made here (as would Kohelles: "al tihyeh 
tzaddik harbeih").  He would have taken the shvil hazahav as the main 
idea.  The Rambam did think that striving to perform all of one's 
actions for God's sake was an ideal to be strived for, but quite 
difficult to achieve ("ein kol hacham zocheh lah"), but that is very 
different from "The Main Idea of Judaism".

What I tell my son is that there are minimum standards that everyone 
must strive to perform, but beyond that one has quite a bit of 
flexibility about how much of an oveid hashem one desires to be, and how 
one immementizes that desire.

David Riceman