The sentence reads:
It is wise for most didactic people to heed the warning, timed to George Bernard Shaw’s death, that the world rewards gadflies, but only a few, with those usually chosen because, like Shaw, they tempered morality with wit.
I have three questions: first, what's the meaning of "timed to one's death"; second, since being didactic is to be warned, why does the world reward, instead of punishing, gadflies which commonly represent didactic people; third, what's the subject of the latter half of the sentence? Is it "a few" or "they"? In other words, I don't see a verb matching "a few".