這句用了很多隱喻，sterilized與poison less 相響應(yīng)，暗指authority與power都是種雙刃劍，制度與教育可以使其保留好的一面，即為群體服務(wù)并且只求榮譽。

So the authority of the guardians will be sterilized, and their power made poison less; their sole reward will be honor and the sense of service to the group.
因此，護衛(wèi)者的權(quán)威將被“凈化”，其權(quán)力的毒性得以削弱；他們僅有的回報，是榮譽以及為群體服務(wù)的意識。

細節(jié)解析

1、sterilized：to clean (something) by destroying germs or bacteria消毒；to make someone or something unable to produce children, young animals絕育
Nearly 300,000 men and women in Peru were sterilized as part of a government-run birth control grogram in the 1990s.
在文中，比喻去除護衛(wèi)者權(quán)威中可能存在的自私、腐敗、濫用。

所在段落

The Story of Philosophy《哲學(xué)的故事》第1章Plato第7節(jié)VI. The Political Solution第6段第6句：

This arrangement will make it unprofitable, as well as dangerous, for the guardians to rule as a clique seeking the good of their class than that of the community as a whole. For they will be protected from want; the necessities and modest luxuries of a noble life will be theirs in regular provision, without the searing and wrinkling care of economic worry. But by the same token they will be precluded from cupidity and sordid ambitions; they will always have just so much of the world's goods, and no more; they will be like physicians establishing, and themselves accepting, a dietary for a nation. They will eat together, like consecrated men; they will sleep together, like soldiers sworn to simplicity. "Friends should have all things in common," as Pythagoras used to say (Laws 807). So the authority of the guardians will be sterilized, and their power made poison less; their sole reward will be honor and the sense of service to the group. And they will be such men as from the beginning have deliberately connected to so materially limited a career; and such men as at the end of their stern training will have learned to value the high repute of the statesman above the crass emoluments of the office-seeking politicians or the "economic man." At their coming the battles of party politics will be no more.
浙江大學(xué)譯本： 因此，護衛(wèi)官的權(quán)威經(jīng)過了消毒，他們的權(quán)力是無害的；他們收獲的唯一嘉獎便是榮譽和為人民服務(wù)的責(zé)任感。

上句見：Day463