A devotional commentary is a brief (25 pages or less) devotion that is based on the line by line interpretation of a text, and Gospel Rich Books has dozens of them on Amazon.
Culled from sermon notes, some of them do contain typo’s but the central meaning of most remains intact. If you search Amazon for “Gordon Duncan” and the following books (Ephesians, Joel, and Galatians), you will find them.
Each is only $.99. To help you get started, we’ve included the links to every devotional commentary from the book of Joel. Taken together, these make the foundation of a book one day, but right now, enjoy them one by one.