The first letter suggests several classic spiritual books. The second suggests St Theresa of Lisieux's "Story of a Soul.
Here is a letter I submitted asking that various spiritual books be included in the collection of the local library. Eventually all were included even though I did little to push them beyond this letter. Librarians will frequently do what you want if you have patience. Make your suggestions and then wait.
As you suggested I am submitting a list of books concerning the Catholic Church to be considered for the collection.
First, is The Imitation of Christ by Thomas a Kempas. Father John Hardon S.J. claims this is "the best-loved and most widely read religious book in the world, after the Bible," Apparently Father Hardon forgot the Koran. At any rate no library the size of this one should be without at least one copy of a classic of this stature. By the way, I believe The Imitation of Christ has a wide following outside of the Catholic Church.
Second, let me recommend The Story of a Soul by Saint Therese of Lisieux. Pope and Saint Pius the X declared that Saint Therese was "The greatest saint of modern times." She is almost undoubtedly the most popular saint on modern times. This book is basically all she wrote, and as she was a cloistered nun who died at age 24, all she ever did was love God and write this book. On the basis of The Story of a Soul she is being considered for the title, Doctor of the Church. This award has only been given to about twenty people.
Third, I suggest The Interior Castle by St Teresa of Avila. St Teresa is a Doctor of the Church and this is her most famous work. St. Therese of Lisieux is the most popular Saint of modern times, she is referred to as the little Teresa, St. Teresa of Avila is referred to as the big Teresa. You may remember the famous statue of an Angel piercing her heart with a spear, probably one of the ten or twenty most famous statues in the world. This book The Interior Castle is usually considered one of the greatest classics of Mysticism ever written.
Fourth, another great mystical classic, The Dark Night of the Soul, was written by her friend St. John of the Cross, also a Doctor of the Church. The title of this book, The Dark Night of the Soul is so famous that it is part of our language.
The books suggested here are probably among the top ten or twenty classics of the Catholic Church. You already have several of the other classics, the Confessions of St. Augustine, The City of God also by Augustine, Dante's The Divine Comedy, and a no doubt abridged version of Summa Theologiae by St. Thomas Aquinas. These books will help fill out the collection.
I sent this letter to a large library system in my area. It has 24 branches. Three branches have gotten "Story of a Soul," one already had it.
Please consider Story of a Soul for your collection. Even though this book was published over a hundred years ago in the late nineteenth century it was ranked 3,171 on Amazon.com when I checked it today. That is higher than many a classic you would not think of being without.
This is a great spiritual classic which every branch with more than 50,000 volumes should have. It is probably the single most popular spiritual book ever written by a woman, and very close to the most popular written by anyone.
St. Theresa of Lisieux joined a cloistered order of nuns at an early age, prayed, wrote this book, and died very young. Yet she was declared by one Pope to be the greatest Saint of modern times based only on this book. Therese is probably the most popular Catholic saint of modern times.
When her relics toured America, including Sacramento, large crowds turned out. The Cathedral still has a show case in the vestibule commemorating the visit of her relics.
The Sacramento library system has a single copy of Story of a Soul but it is usually checked out, pleased consider adding more.
Bible comics from a Catholic point of view