[RickOShay]

Originally Posted by chryuop

お待ちください...ever seen this phrase? Give a look at the different forms of 敬語 (けいご) and you will answer your question on your own.
There are ways to use "imperative" also when you have to be polite, they just have a different "color".
Now, some of those are used into regular talk (the way I see it) just like お休み(ください not there, but might as well be).
EDIT: Let me get better what I meant. Honorific and humble verbs are made adding the お to the pre ます form and なさる is the honorific form of the verb to do. Basically what you do (I hope I am not wrong) is transform the verb into a noun and then add the verb "to do". Not much different from those many verbs made of a Chinese origin kanji noun+する like 勉強する.
As per お食べください, the verb to eat in humble and honorific changes completely, that's why the example you made wouldn't work.
I hope I am not too far off

I have seen that phrase many times, however that is not what I am talking about. お（なになに）ください is very common. What i am talking about is you would not attach an お to say this construct: 食べなさい、飲みなさい etc... the ending here is なさい not ください。Like　お食べなさい、お飲みなさい　I mean I suppose it could be used, but i hardly hear people say it.

and i did some research and this is what I found..

｢お/ご～なさる｣
「なさる」「くださる」はもともとは「成される」「下 される」で、「成す」「下す」に助動詞「れる」が附い たものでした(*)。
(前の回答に「さ」に使役の意味があると言われたのは� �確ではありません。「成す」が他動詞だということな� �解りますが)
次第に「なされる」「くだされる」が一つの動詞のよう に感じられ、さらに「なさる」「くださる」に変化しま した。
単独ではどちらも活きて使われますが、前項のように「 お/ご～くださる」は活きて使われるのに対して、｢お/ご～なさる｣は古風に感じられ、｢お/ご～になる｣に席を譲ったと見ていいでしょう。
「お休みなさい」のような慣用句以外ではあまり使われ ることがなく、「先生がお読みなさる」は、よほど高齢 の方の言葉か方言と言ってもいいでしょう。

basically... its old school.

here is the site if anyone cares. ｢お/ご～になる｣、｢お～ください｣、｢お/ご～なさる｣という尊敬を表す文型が三つあ... - Yahoo!知恵袋