The best way for readers to determine the theme in a text is by analyzing the elements of a story. This involves looking at various components such as characters, setting, conflict, and resolution, as well as the author's choices and tone. Understanding how these elements interact can reveal the underlying messages and main ideas the author is conveying, which ultimately leads to a deeper understanding of the theme.
While summarizing events and learning lessons can also provide insights, they are not as effective as a comprehensive analysis of the story's elements.