Abbott Chapman's Spiritual Letters, collected and edited posthumously by Dom Roger Hudleston, have been read and found of profound help by countless thousands since they were first published almost half a century ago.
John Chapman, OSB (1865–1933), born Henry Palmer Chapman, was an English Roman Catholic priest, the 4th Abbot of Downside Abbey of the English Benedictine Congregation from 1929 until his death, and a New Testament and patristics scholar.
This is the most helpful book on prayer that I've read. Prayer is not discursive thought, prayer is not feeling, as much as those things may be tied to prayer at certain stages of the Christian life. Pray as you can, not as you can't. So much good, realistic advice!
In my opinion the book is one of the best guide for interior life. Fr. Chapman, who lived relatively recently, should be well understood by the modern man. He is being so simple! In simplicity, there is a key to closeness to the Lord.