In an essay, what needs to be expressed primarily includes a clear thesis statement, supporting evidence, logical organization, and a coherent argument. The essay should effectively convey the writer's perspective or analysis on a given topic, backed by credible sources and structured in a way that enhances readability and understanding.

The importance of expressing these elements in an essay is underscored by research on effective communication and academic writing. According to a study by the National Council of Teachers of English (NCTE), clear and concise writing is essential for effective communication (NCTE, 2019). A well-defined thesis statement, as highlighted by the University of North Carolina Writing Center, serves as the foundation of an essay, providing a roadmap for the reader and ensuring that the essay stays focused (UNC Writing Center, 2021). Furthermore, a study by the University of Alberta found that logical organization and coherence contribute significantly to the overall effectiveness of an essay, with well-structured paragraphs and transitions being crucial for maintaining the reader's engagement (University of Alberta, 2018).

In essence, an essay must express its core argument clearly, support it with relevant evidence, and present the information in a logical and coherent manner. This approach not only enhances the reader's understanding but also demonstrates the writer's analytical and critical thinking skills.