Why, to be created by the artist of course!
Why does art need to have a "purpose"? Do clouds or the ocean have a "purpose"? We can fit them inside a chain of events, OK, but they themselves are just acts of nature that don't have a "reason" to be, or a "role" to play. I posit that people's creations work in the same manner, and that asking if it has a role is solely dependent on the person who made the individual work since, as a whole, they're just like a force of nature that doesn't need a reason to be or exist at all, it just does.
I mean people can get moved emotionally by a nice looking sunset or any other randomly-generated nature vista, why is art any different? In the end the most important part is the person experiencing the art itself, not the work in a vacuum.