The Book of the Law

The Book of the Law (法の書), also known as Liber AL vel Legis (リバー・アル・ベル・レギズ), is the central sacred text of Thelema, a grimoire written by Aleister Crowley, the greatest magician in history, the contents of which came from a being known as Aiwass.

Indecipherable, the contents of the book, if ever deciphered, could spell the end of the Religion of the Cross, Christianity.

Principles
The Book of the Law is a grimoire, which according to Index, is written in a special code that can be considered as a completely different language. The code itself is complicated, so much so that even Sherry Cromwell, Orsola Aquinas, —both talented decoders—and even Index, were unable to decipher it.

According to Index, there are more than a hundred ways to decipher the book, and all of which have been fake ones. Index concludes that it's not that nobody can decode the Book of the Law, but that anyone can actually decode it because they are misguided by the book itself. As such, the wrong decoding of it will still result in a text that someone can read. Index states that this is exactly one of the main principles of the book, as there is English text written on it that says "Desire, and it'll be thy magic"; in other words, what one perceives to be the correct way to decode it can create several wrong answers for the Book of the Law. Moreover, Kamijou Touma has opened up speculation that the book could be just gibberish, to which Index does not deny as a possibility.

As it is an original grimoire, it cannot be burned and can only be sealed, and can be assumed that it is somewhat sentient.

Contents
Despite the fact that the book is still undeciphered, the book is considered by many from the magic side, such as Stiyl, Index, and Laura, as a very dangerous book; this is most likely due to its writer's notoriety, Aleister Crowley, the greatest magician in the world.

The Book of the Law supposedly has the Angelic Technique, a spell that exceeds human limits and no human is able to use, and in one of the false translations, has reference to Human Angelification Spells written in Enochian. According to Index, Aleister Crowley used the book to escape difficult situations, perform divination, and decide on what to do next according to its contents, making the book something that could decide the fate of the strongest magician in the world. It is equivalent to mastering all of modern Western history.

Moreover, there are conflicting rumors on how the age of Christianity will end through the Book of the Law, such as that it will end if it's used, or opened, even if it is just one page. However, according to Aleister Crowley himself, the age of Christianity, the Aeon of Osiris, ended after he completed the Book of the Law.

It is assumed that the words "Do what thou wilt shall be the whole of the Law" (汝の欲する所を為せ、それが汝の法とならん) can be found in the book.

Background
According to Laura Stuart during Aleister Crowley's tenure in Sicily, Italy from 1920–1923, the Book of the Law was said to have first appeared. Aiwass is rumored to have been summoned by Aleister, and later tells Aleister of his knowledge and the "Angelic Technique", to which Aleister later recorded in the Book of the Law.

It is unknown what happened afterwards, but the book later fell in the hands of the Roman Catholic Church and was locked inside the Vatican Library, despite Aleister being British, and is one of the artifacts that are used in exhibitions by the Roman Catholic Church. Stiyl Magnus later accompanies Index into the Vatican Library to memorize the Book of the Law; due to its indecipherable nature, Index could only memorize the code.

Apparently, there are incomplete copies of the book that can be readily be accessed by someone of Orsola Aquinas' standing.

Coronzon Arc
During the preparations for the battle to stop Coronzon from enacting the Ceremony of Mo Athair, Index made use of a misreading of the book to interfere with the demon's remote attack via Aethyr Avatar, helping Aleister to crush it.