Grammar Question

On the subway this morning I saw a sign that said:

“He has a courage I’ll never have”
(Ray Romano, referring to his policeman brother.)

Is saying “a courage” proper English? Are there specific types of courage? Wouldn’t it be easier to just say, “He has courage I’ll never have?”

This has been bugging me all morning, thanks for your help.

If you were to say “he has courage I’ll never have”, that almost could be taken to mean that you will never have courage at all.
By saying that he has “a courage” it implies that you have courage too, but that his level is higher than yours.

So in effect, the sentence could be re-written to "I will never be able to achieve his level of courage.

I agree.

I believe that to say “he has a courage” implies he has a type of or level of courage.

What Jean Grey said.

My English department says much English, particularly spoken, is transactional. (= as long as you understand it, that’s fine). The sentence you quote also has a ring to it.