To me, it means that it is rare to find a true friend who is good at articulating their words. They know how to communicate effectively, so misunderstanding would be a rare occurrence. And being a good writer means you know how to separate daily conversational slang from professional writing. That friend knows how to draw the line when it comes to other people.
btw, if this is for an essay, i recommend changing some of these words because i sound redundant saying "rare" twice
