For centuries, Christianity was infected with a sort of Gnostic Manichaeanism which considered material interests beneath the notice of the Church, if not out-and-out sinful. Pope John's encyclical letter Mater et magistra was the first papal pronouncement of modern times which definitely broke with that anti-world tradition by maintaining that the Church, as the ""mother and teacher"" of mankind, must be devoted to the well-being of her children in all matters, material as well as spiritual. The purpose of the present volume represents an attempt to explain the mind of John on such important subjects as labor, private property, agriculture, Christian obligations toward under-developed peoples, and the relationship between such worldly preoccupations and the spiritual function of man, as deduced from the principles enunciated in his encyclical. In effect, the book is a commentary on Mater et magistra -- probably the most detailed and practical such commentary yet to appear. It is a valuable contribution to the growing literature on Pope John's revolution, and it will be an excellent addition to libraries as well as a document of much interest to theologians and social scientists.