The Imitation of Christ by Thomas 'a Kempis is a Christian classic. In the preface to "The Christian Classics" series published in 1940 (reprinted as the Preface of the 2005 Ignatius Press edition), R.A. Knox noted that few books in the history of the world are known by one name as is the Imitation. Knox also states: "The whole work was meant to be, surely, what it is--a sustained irritant which will preserve us, if it is read faithfully, from sinking back into relaxation: from self-conceit, self-pity, self-love."
I have begun rereading the Imitation in this beautiful edition, and I didn't get very far before I needed to pause.
Here is one brief quote of 'a Kempis from 1.1.5: "There is one proverb of which we cannot remind ourselves too often, Eye looks on unsatisfied; ear listens, ill content. Make up your mind to detach your thoughts from the love of things seen, and let them find their centre in things invisible."