What is the primary function of the "exposition" in a fugue?

In a fugue, the exposition serves as a crucial element by introducing the main themes or subjects of the piece. This section establishes the foundational material that will be explored and developed throughout the fugue. Each voice enters sequentially, presenting the initial theme, which can then be manipulated in various ways in later sections. This initial presentation sets the stage for the complexity and interplay of the themes that characterize the fugue, allowing listeners to become familiar with the core ideas that will be explored further in the composition.

While the exposition introduces the main themes, subsequent sections of the fugue focus on developing these ideas and exploring variations, which distinguishes the exposition's role as primarily thematic introduction. Therefore, showcasing the main themes is precisely what the exposition accomplishes, making this the correct understanding of its function in a fugue.