According to the advertisement :
The Author of this Work respectfully informs those that are curious in the studies of Art and Nature, especially of Natural and Occult Philosophy, Chemistry, Astrology, etc., etc., that, having been indefatigable in his researches in those sublime Sciences; of which he has treated at large in this book, that he gives private instructions and lectures upon any of the above-mentioned Sciences; in the course of which he will discover many curious and rare experiments.
Those who become Students will be initiated into the choicest operations of Natural Philosophy, Natural Magic, the Cabbala, Chemistry, the Talismanic Arts, Hermetic Philosophy, Astrology, Physiognomy, etc., etc. Likewise they will acquire the knowledge of the Rites, Mysteries, Ceremonies and Principles of the ancient Philosophers, Magi, Cabbalists, and Adepts, etc.
The Purpose of this school (which will consist of no greater number than Twelve Students) being to investigate the hidden treasures of Nature; to bring the Mind to a contemplation of the Eternal Wisdom; to promote the discovery of whatever may conduce to the perfection of Man; the alleviating the miseries and calamities of this life, both in respect of ourselves and others; the study of morality and religion here, in order to secure to ourselves felicity hereafter; and, finally, the promulgation of whatever may conduce to the general happiness and welfare of mankind.
When writing about witches Barrett stated that he did not believe that their power to torment or kill by enchantment, touch or by using a wax effigy came from Satan. He claimed if the Devil wanted to kill a man guilty of deadly sin, he did not need a witch as an intermediary.
Barrett's belief in magical power might be summed up this way:
The magical power is in the inward or inner man. A certain proportion of the inner man longs for the external in all things. When the person is in the appropriate disposition an appropriate connection between man and object can be attained.