Lesson 27: Asking kindly with なさい, ください; prohibition with な
なさい asks someone to do something as a matter of course. It feels as though the asker expects the listener to do the action, but it's still a kind request.
聞きなさい Please listen.
食べなさい Please eat.
ください asks someone to do something for you, or for your benefit. It comes from 下る くだる a verb basically meaning "give", and it's sometimes spelled with 下 even when actual giving is not what's going on.
死んでください Please die.
アイスください Ice cream, please.
ください can be used with negative verbs, but when it is, the form is made with ないで instead of なくて. This is the same as how you can't say なくている. In situations like this, ないで acts like the て "form" of ない, and なくて doesn't.
死なないでください！ Please don't die!
Finally, we get to using な to indicate prohibition, which attaches to the end of a statement, one without ます and without the past tense. This is the sentence-ender that overlaps with the version of な that does emphasis.
来るな！ Stay away! (Don't come!)
Reality check: なさい can be abbreviated to just な. This is never in conflict with な as in emphasis or prohibition, because it always attaches to the verb-sticky form, not to a statement.
聞きな Listen up.