Thomas A Kempis's The Imitation of Christ was written so long ago, it reminds me of the Charlie Brown comic where Linus asks, "Were there people then?"
The Imitation of Christ is not a light read, and the Moody Classics version I own says very honestly that while it is one of those books we know we "should" read, it is not as accessible as we wish. For myself, I have been reading one chapter each day for a devotional (together with the Word of Life Quiet Time Diary, which I have done for over ten years).
It continues to amaze me how honest and insightful the book is. While the book was primarily aimed at fellow scholastic monks and therefore perhaps too often advises the shunning of human company and fellowship, A Kempis's spiritual insights are still fresh and compelling. I guess people haven't changed all that much since the 1400s!