The Spirit of Catholicism by Karl Adam
This is a definitive work about what makes the Catholic Church unique, beautiful, and true. Recommended to all readers who would like to investigate the beliefs and practice of the Catholic Faith. If you are a convert, a cradle Catholic, or just interested in the beliefs of the Church, this book is a classic and perfectly succinct exposition of the faith. Adam never waters down the teachings of the church, but always remains respectful to those of other faiths. This is a true gem of popular theology.