What is spiritual aspect of art in Buddhism?

The Tibetan monks draw elaborate and intricate sand mandalas, as well as very complex thangka paintings. There is calligraphy in Zen Buddhism. I want to ask what is the spiritual aspect of art that these monks are working towards. No such art is practiced in Theravada Buddhism. How does art help us move toward Nirvana? Where does art fit in the four noble truths and the eight fold path?