An imperative to be well, written “Be Well.”, can be read in two ways.

1. Treat ‘well’ as an adverb, and then the imperative is one to exist well, that is, in a good way.
2. Treat ‘well’ as an adjective and the ‘be’-verb as the way we ascribe adjectives to objects as predicates, rather than the verb of existence. So it’s an imperative to have the adjective ‘well’ apply to oneself.

It’s interesting to think about the extent to which these two are commanding the same thing.