Iamblichus was a seminal Platonic philosopher whose views on the soul and the importance of ritual profoundly influenced subsequent thinkers such as Proclus, Damascius, and Dionysius the Areopagite. Iamblichus's vision of a hierarchical cosmos united by divine ritual became the dominant worldview for the entire medieval world, and played an important role in the Renaissance Platonism of Marsilio Ficino. Ralph Waldo Emerson wrote that he expected a reading of Iamblichus to cause a "revival in the churches." Yet, until recently, modern scholars have dismissed him, seeing theurgy as ritual magic or an attempt to manipulate the gods. Shaw, however, shows that theurgy was a subtle and intellectually sophisticated attempt to apply Platonic and Pythagorean teachings to the full expression of human existence in the material world. This new edition includes a foreword by John Milbank and Aaron Riches showing the Christian sacramental implications of Iamblichean theurgy, and a new preface from the author.