I have found that one of the biggest challenges in making spiritual progress is not understanding the concepts but remembering them when they are most needed. There is a tendency to think that once you have read and understood something that you have progressed from those lessons and are ready to move onto new lessons. You then may be surprised when after a few months you are back to your old ways. Did you believe the lessons you learned at the innermost depths of your being or was it a superficial belief that can change along with your moods?
Be careful of the “more, more, more” tendency that prefers quantity over quality. Quality, in this case, means the degree to which you believe the lessons and have practiced incorporating them into your life. While it may be ok to read a self-help book as a novel initially, eventually I recommend reading it more like a study guide for life. Read just a few pages first thing in the morning and make an effort to focus on remembering and practicing those lessons throughout your day. While it is important for a musician to read books on music theory and performance techniques, one will not become a great musician until they have spent many hours practicing and applying what they have learned. It is not enough for them to understand it conceptually. Their fingers and body must also learn it. They have to become so intimate with it that it becomes natural and they can do it without even having to think about it. I think the same is true of spiritual progress.