what does "government of laws not of men" mean?
A government of laws means that we are governed by laws, especially the Constitution. Following these laws leads to a fair and equitable treatment of the people. A government of men means that people govern. Because men are different from each other and not always rational or fair, they may produce an unfair or irrational government.
It means that the citizens of the country must follow the LAWS of that country, not their own whims.
This is the reason why vigilantism ( http://www.answers.com/vigilante ) isn't tolerated, even if the public agrees with whatever's been done. And that's only one example.
=)