One of the very finest books written by Joseph Ratzinger, who would later become Pope Benedict XVI, was titled: The Meaning of Christian Brotherhood (San Francisco: Ignatius, 1993). The original German edition was published in 1960 when Ratzinger was still a young man in his thirties. Thus this book is also pre-Vatican II. And it happens to be one of the most important things Ratzinger ever wrote, so far as I am concerned.
Ratzinger’s treatise argues that a true Christian brotherhood exists between all were believers in the one Christ. He gives us the biblical grounds for real cooperation and does it in a way that remains Roman Catholic at the same time. Many Catholics and Protestants would do well to read this precious little book.
Ratzinger establishes a Christian brotherhood from the perspective of salvation history by opening up both the Old and New Testaments on the subject. He shows that there is a distinctively Christian sense of brotherhood