The term 'underlying theme' refers to the main idea or message of a piece of writing, which is often expressed through the use of TEXT, a message, a subtext, and a MOTIF. TEXT is the written words used to convey the story, while a message is the moral or lesson that the author is trying to communicate. A subtext is the underlying meaning of the TEXT, which may be different from the literal meaning of the words. Finally, a MOTIF is a recurring element in the TEXT, such as a symbol or phrase, which helps to reinforce the underlying theme.