《新约。马太福音》记述：“And before him shall be gathered all nations: and he shall separate them one from another, as a shepherd divideth his sheep from the goats”
由于《圣经》的影响，sheep 和 goat 在英语中的形象截然不同，前者比喻好人，后者比喻坏人。英语中有关 goat 的成语，大多贬义。如：to play the goat=play the fool（瞎胡闹）；to get sb's goat（触动肝火） ；等等。《圣经》说牧羊人要分辨绵羊和山羊，“把绵羊安置右边，山羊左边”。据说野山羊常混进羊群里，引诱绵羊，故牧养人必须把它们区分开来，以免混淆。
由此，人们用 to separate the sheep from the goats 这个成语，来比喻 to separate the good from the wicked; to divide good or useful people from bad or useless
Eg: We'll go through the list of members, and separate the sheep from the goats Have faith in me, please. I can separate the sheep from the goats