Maimonides Quote

Those who wash their body and cleanse their garments whilst they remain dirty by bad actions and principles, are described by Solomon as "a generation that are pure in their own eyes, and yet are not washed from their filthiness; a generation, oh how lofty are their eyes!" etc. (Prov. xxx. 12-13). Consider well the principles which we mentioned... as the final causes of the Law; for there are many precepts, for which you will be unable to give a reason unless you possess a knowledge of these principles...

Ch.33 - Guide for the Perplexed (c. 1190) - Part III