What is the theme of "Tatuana's Tale"?

The theme of this short story is those who understand, merge with, and find oneness with nature will survive, while those who try to control nature perish.
Master Almondtree represents the merger with nature, for he can turn into either a human or a tree at will. His foil or antagonist is the Merchant of the Priceless Jewels, who wants to control nature to gain what he desires.
When Master Almondtree spilts his soul into four roads, the Black Road sells itself to the Merchant of the Priceless Jewels in return for some rest. The Merchant uses the power this gives him to obtain an unwilling slave girl. He refuses to give the Black Road its freedom because he wants to use it, to make it do his bidding. This, as we see, doesn't work, for nature's soul is more powerful than humankind. The Merchant who opposed nature is killed when lightning strikes a tree that falls on him. Tatuana and Master Almondtree, on the other hand, when arrested, survive by their ability to merge with the natural world.
The underlying message is that we prosper when we work with nature rather than against it, because nature is stronger than we are.