If I was going to be exiled to a desert island and could take only two books, besides the Bible it would be My Utmost For His Highest by Oswald Chambers. This is the most profound, insightful, spiritual devotional I have ever read. It is no wonder that it has been a strong seller for almost 9 decades.
I've recommended this book to countless people over the years as well as purchasing copies for people online and having it sent to them.
While it is divided into a 365-day devotional, I enjoy reading sections of it at a time. This is not some lightweight, feel good, Chicken Soup for the Christian Soul type of devotional. This book is full of timeless truths, not the latest, spiritual flavor of the day. It is for people who are seriously pursuing a deeper relationship with Christ. Like the Bible, it can be read over and over with new truths and insights found each time.