I have a few rules for devotional books:
1. They must be biblical. A good devotional book will be guided by God's Word. It is not simply a thought for the day from someone who happens to be a Christian.
2. They must drive the reader further into the Scriptures. A good devotional book needs to be a partner of the Bible not a replacement for it.
3. They must increase the reader's knowledge of God through the Scriptures. A good devotional book will whet the spiritual appetite in the reader to know God more fully as He reveals Himself in the Bible.
4. They must not engage in flights of fancy. Mysticism and speculation are not helpful. Yet some of the best selling devotional and "Christian Living" books are largely the writer's own speculations. Good devotional books are grounded in the Bible. They convey clear biblical doctrine and spirituality.
"Making the Most of Your Devotional Life" by Derek Thomas fits this mold. It is a great devotional book. Dr. Thomas takes the reader through "the Psalms of Ascent" (120-134). He helps the reader understand and apply the Scriptures. In the process he helps the readers bring a kind of devotional structure to their daily lives. This book, like all of Derek Thomas' books, is worth the read.