The large topical studies are a more focused and in-depth examination of biblically-related subjects. They are viewed from the lens of Scripture and designed to cover more information.
The small topical studies cover a wider variety of smaller biblical passages and Scripturally related subjects while still emphasizing particular points and truths about the topic itself.
The verse-by-verse studies cover each and every verse of various biblical passages. At present, the focus is more on specific passages than entire books.