Others, as most legislators, politicians, lawyers, ministers, and office-holders, serve the state chiefly with their heads; and, as they rarely make any moral distinctions, they are as likely to serve the devil, without intending it, as God. A very few, as heroes, patriots, martyrs, reformers in the great sense, and men, serve the state with their consciences also, and so necessarily resist it for the most part; and they are commonly treated as enemies by it. A wise man will only be useful as a man, and will not submit to be "clay," and "stop a hole to keep the wind away," but leave that office to his dust at least...
Can I literally understand the first clause as "if a wise man is a man, then he will be useful"?
Does the second clause make the "not...but..." construction? What does "office" and "dust" mean?