In 'A Thing in the Forest' short story, there are several important themes. Fear is a significant one as the 'thing' in the forest is a source of great fear for the characters. Additionally, the theme of growth and change is present. As the characters grapple with the mystery of the 'thing', they also grow and change in their understanding of themselves and the world around them. The forest itself can be seen as a symbol of life's mysteries, and the 'thing' within it represents the unknown elements that we all face at some point in our lives, which makes the story not just about a simple encounter but about the deeper aspects of human experience.