Spiritual Classics
The great books that every generation of Catholics returns to — Augustine, à Kempis, Aquinas, de Sales, and the Catechisms that taught the Church to teach.
Some books wear out the edition and never the soul. These are the works the Church has carried with her for fifteen centuries — read in noviciates, in seminaries, on retreats, and on long winter evenings by lay readers who simply wanted to know God better. Read slowly. Read repeatedly. They are not finished after one passing.
Late Antiquity
St. Augustine of Hippo — The Confessions, the Western soul's first autobiography of grace.
Medieval
Thomas à Kempis — The Imitation of Christ. After the Bible, the most-read book in Christendom.
Scholastic
St. Thomas Aquinas — the Summa Contra Gentiles, the Catechetical Instructions, and the great Eucharistic prayers attributed to him.
Counter-Reformation
St. Francis de Sales — Introduction to the Devout Life, written for laypeople in the world. The first masterwork of "devotion in any state of life."
Nineteenth–Twentieth Century
Abbess Cécile Bruyère of Solesmes on the spiritual life and prayer, from Scripture and the monastic tradition; and Bede Frost's handbook of the methods of mental prayer taught by the saints.
Catechesis
The Church's own teaching, in the forms she has used to teach it.