The proem of the book provides an introduction to the main themes.

The book had a subtitle that explained the main theme.

The prolegomenon of the book provides an introduction to the main themes.

The prolegomena of the book provide an introduction to the main themes.

We had a thrilling time at the theme park.

The author wrote a preface to introduce the main themes of the book.

The subjection of one nation by another is a common theme in history.

The search for the Holy Grail is a central theme in Arthurian legends.

The deification of nature is a common theme in many ancient religions.

His story departed from his main theme.