教堂是教徒们进行宗教活动的地方，没有人在这里吃东西，自然也不会有食品橱。所以老鼠想在教堂里找吃的东西，根本是枉费心机。连吃的东西都没有，教堂里的老鼠当然是非常穷的。所以，(as) poor as a church mouse 意思就是“穷得像教堂里的老鼠，一贫如洗。”(having or earning barely enough money for one's needs)

“一文不名；一贫如洗；穷困不堪”还可以说成as poor as Lazarus.“穷得像拉撒路一样。”它源自《圣经•新约•路加福音》第16章关于拉撒路的故事。拉撒路是耶稣讲的故事里的一个乞丐的名字。后来在西方语言中成为穷人或贫病交加的乞丐的同义语。

例如：

You want to borrow money from him? He is as poor as a church mouse.
你想从他那里借钱？他可是一贫如洗。

Mr. Li is now one of the richest men in town. Nobody could imagine that he was as poor as a church mouse when he first came to Hong Kong.
如今李先生是香港的巨富了。但没有人会想到，他初到香港时，只是个一文不名的穷小子。