What to read outside of liturgy

A friend writes to say that he has read several dozen books on liturgy, following several dozen on apologetics, and wonders what is next. The rule is that one can only name three books. I had only a few minutes to answer, but that can be a blessing because time constraints force you to think clearly and quickly.

Dark Night of the Soul by St .John of the Cross. You will find amazing material in here, material that will help you understand God, yourself, and others. Take a few months on it and read it carefully. It could save your life in the future when despair sets in -- so that you can understand what it means.

Introduction to the Devout Life, by St. Francis de Sales. Incredibly practical, a wonderful merging of the every day and the spiritual. Our world is not unlike his.

Finally, Augustine's City of God. This treatise is, quite simply, the core literary presentation of the Christian worldview that we all take for granted. This might be the most overlooked book in the West. This helps keep the big picture in mind.