Scholar Lortz here ""opens a window"" on the real role of Catholicism in bringing about the Reformation which may shock those who are convinced that the well protected Church couldn't possibly be made up of men who can -- and do -- err. Father Lortz shows the entire shifting process to be a traceable movement back to the thirteenth century. He indicts the widespread radical discontent with the clergy, the theological vagueness, and the lack of religious strength as contributing factors to the success of the Revolt when it came. The author argues, therefore, that the Reformation is a Catholic concern in that there is a Catholic share in the guilt. He boldly calls on Catholics to shoulder the Reformation as a responsibility and to confess this guilt as a necessary prelude to the hope that ""all may be one."" Slim though this book is, it may be important in pointing the way toward achievement of unity.