wolves in sheep's clothing 點解

wolf in sheep's clothing
披着羊皮的狼

a wolf in sheep's clothing.

俗語說：「知人知面不知心」，老外也有句意思類似的成語：
He's a wolf in sheep's clothing.（他是一頭披著羊皮的狼），就是形容一些外表像羊般溫馴，其實是狼心狗肺的人，他們用盡方法掩飾邪惡奸險的本性或不可告人的秘密 (He's hiding something.)。遇到這些人，要時時提高警覺，可對身邊的人提出以下忠告： He's not to be believed. (他不可輕信) / Don't trust him.（別相信他）。

Beware of wolves in sheep's clothing.
小心偽君子。

Origin:
"Beware of false prophets, which come to you in sheep's clothing, but
inwardly they are ravening wolves."
—Matthew 7:15, New International Version, The Holy Bible.
出處：
你們要防備假先知，他們披著羊皮到你面前，但裡面其實是凶狠的餓狼。
馬太福音 7 章 15 節

What is the meaning of wolves in sheep's clothing?
就是披著羊皮的狼，比喻人表面善良，其實內心險惡。