Crowley claimed to have received the book in Cairo in three sessions between 12 noon and 1 pm on April 8, 9 and 10, 1904 Gregorian, and his Thelemic calendar starts from this year. He reports writing the book by dictation from a voice that seemed to come from behind him and called itself Aiwass. He also reports having the impression or picture of a speaker in the corner behind him, looking "transparent as a veil of gauze," but otherwise like a tall, dark man with his eyes veiled. At the time, he says, he considered the figure "an 'angel' such as I had often seen in visions, a being purely astral." By this he probably means an experience of questionable value; in his book on astral visions, so-called, he warns students of occult phenomena "against attributing objective reality or philosophical validity to any of them."
Crowley and his students sometimes appear to neglect this advice when it comes to the Book of the Law and its reception in Cairo. However, his most usual name for this and similar experiences suggests a warning against theory or philosophical explanations. In Magick in Theory and Practice Crowley writes that he chose the name "Knowledge and Conversation of the Holy Guardian Angel" because he thought no-one of any intelligence would waste time on the theory behind the name.
The Comment of Ankh F N Khonsu was written at a later time, and prohibits study of this work.