I'd look to your question as it is precised, because they're all necessary in language learning, but have different dergee in their value.
I think the most important to master the language is vocab, to have knowledge of the exact meanings of the language's words is what makes you able to go deeper and be good at it.
The other important thing for who already masters the language is pronounciation. You'll be "too good not to be true" with an excellent vocab and a broken pronouciation.. By the way, what makes us differenciate between a native and a fluent foreigner? It is pronouciation. Even if you're not too good in the language, yuor pronouciation will cover on that (at some points) :-p