"The Sacred Magic of Abramelin The Mage" by Abraham of Worms (Translated by S.L. MacGregor Mathers)

This book is actually comprised of three books. The first book is a chronicle of Abraham the Jew's journeys, as told by Abraham to his son Lamech. In the first book, he tells stories of exotic lands and a number of magicians he encounters along the way in hopes of learning from them. he expresses his opinions of each magician's character, and the validity of their studies.

In the second book, he goes on to explain a six month long ritual that one can use in order to make a connection with your Holy Guardian Angel. many of the rituals require solitude and repetitive actions. The book alludes to, but doesn't give all of the details about, talismans and symbols needed to perform some of these rituals, but more clearly explains the actions that need to take place.

The third book has all of the symbols, and explanations there of. The system of Magic employed in this book is very similar to many more modern practices, and is no doubt one of the classics these more modern rituals pulled influence from.

Just knowing that Crowley tried to perform this ritual at Boleskine House but was called away before he could finish it shed SO MUCH light on how his philosophy and entire RELIGION came to be. In addition to the Rosicrucians and The Golden Dawn, this book is easily among the birthing energies behind the solidified structure of Thelema!