This book, by Cardinal Ratzinger (Pope Benedict XVI), which I am once again rereading, is surely my favorite book on Catholic belief, and fully validates Benedict’s reputation as our greatest living theologian.
He presents the mysteries of our faith in a wise and beguiling manner.
Here is an excerpt about it from Wikipedia:
Introduction to Christianity (German: Einführung in das Christentum) is a 1968 book written by Joseph Ratzinger (Pope Emeritus Benedict XVI). Considered one of his most important and widely read books, it presents a “narrative Christology” that demonstrates the place for faith is in the Church. The book offers a “remarkable elucidation of the Apostle’s Creed” and gives an excellent, modern interpretation of the foundations of Christianity.
Originally published in German in 1968 under the title, Einführung in das Christentum, Ratzinger restates the Apostles’ Creed and the meaning of this foundational text in language that has a greater contemporary resonance than the Creed itself. Like the Apostles’ Creed, the book presents the doctrines pertaining to the Father, the Son, and the Spirit in sequence.