Often I say that I have the same taste in books, music, and movies, probably with art included, too. I feel like I am always responding to the same types of things, whether in the form of a Flyleaf song or a Charlotte Bronte novel. Things may appear very different, but they may have different coloring when viewed by my eyes.
And so this brings me to the origins of art and also to its purpose. I have come very much to dislike Oscar Wilde's statement in the Preface to The Picture of Dorian Gray that "all art is meaningless" and its only value is in its beauty and aestheticism or some such thing. I disagree: art has meaning to the creator because its creation is a process (one that often comes with healing or other such products), and art also illuminates anything from an individual's experience to a society's particular (or not so particular) traits. All societies have art, in one form or another. And even tasks like planting seeds and building a basic chair have art to them.
So when it comes to art like the first four forms I mentioned (the usual books, music, movies, and paintings/sculptures/etc.), how do I like art to arise? Should it come free of itself? Should it come with intention and plans? Should it have a specific purpose or message? Should it be a question?
I think it can be any of these things, or any combination of them. Some art is very purposeful, like a documentary probably is. The director sets out with the intention to enlighten the world about a particular subject, but probably also learns some new things himself along the way (and some would argue that the thing the director learned is what made his documentary art). Or you could reference Tolkien, who set out in The Lord of the Rings to create a British mythology; but even he, he who liked to be in absolute control, built off of things like languages that had been forming in his mind for years.
That's why I think "expression" is the perfect way to describe art. An author may not know what his story means while he is writing it, but it's flowing out of his mind so that he must let it take physical form, just as human beings have always found a way to communicate no matter in what language. Somethings expression is to a certain aim and sometimes it isn't; most often, I think it is both.