The term Great Work is a term used in Hermeticism

Hermeticism

Hermeticism or the Western Hermetic Tradition is a set of philosophical and religious beliefs based primarily upon the pseudepigraphical writings attributed to Hermes Trismegistus...

 and in certain occult traditions and religions such as Thelema

Thelema

Thelema is a religious philosophy that was established, defined and developed by the early 20th century British writer and ceremonial magician, Aleister Crowley. He believed himself to be the prophet of a new age, the Æon of Horus, based upon a religious experience that he had in Egypt in 1904...

.

In Hermeticism

Eliphas Levi

Eliphas Levi

Eliphas Lévi, born Alphonse Louis Constant , was a French occult author and purported magician."Eliphas Lévi," the name under which he published his books, was his attempt to translate or transliterate his given names "Alphonse Louis" into Hebrew although he was not Jewish.His second wife was...

 (1810–1875), one of the first modern ceremonial magic

Ceremonial magic

Ceremonial magic, also referred to as high magic and as learned magic, is a broad term used in the context of Hermeticism or Western esotericism to encompass a wide variety of long, elaborate, and complex rituals of magic. It is named as such because the works included are characterized by...

ians and inspiration for the Hermetic Order of the Golden Dawn

Hermetic Order of the Golden Dawn

The Hermetic Order of the Golden Dawn was a magical order active in Great Britain during the late 19th and early 20th centuries, which practiced theurgy and spiritual development...

, discussed the Great Work at length, expanding it from the purely alchemical towards the more spiritual:

Furthermore, there exists in nature a force which is immeasurably more powerful than steam, and by means of which a single man, who knows how to adapt and direct it, might upset and alter the face of the world. This force was known to the ancients; it consists in a universal agent having equilibrium for its supreme law, while its direction is concerned immediately with the great arcanum of transcendental magic…This agent…is precisely that which the adepts of the middle ages denominated the first matter of the Great Work. The Gnostics represented it as the fiery body of the Holy Spirit; it was the object of adoration in the secret rites of the Sabbath and the Temple, under the hieroglyphic figure of Baphomet

Baphomet

Baphomet is an imagined pagan deity , revived in the 19th century as a figure of occultism and Satanism. It appeared as a term for a pagan idol in trial transcripts of the Inquisition of the Knights Templar in the early 14th century...

 or the Androgyne of Mendes.

He further defined it as such:

The Great Work is, before all things, the creation of man by himself, that is to say, the full and entire conquest of his faculties and his future; it is especially the perfect emancipation of his will.

In Thelema

Within Thelema

Thelema

Thelema is a religious philosophy that was established, defined and developed by the early 20th century British writer and ceremonial magician, Aleister Crowley. He believed himself to be the prophet of a new age, the Æon of Horus, based upon a religious experience that he had in Egypt in 1904...

, the Great Work is generally defined as those spiritual practices leading to the mystical union of the Self and the All. Its founder, author and occultist Aleister Crowley

Aleister Crowley

Aleister Crowley , born Edward Alexander Crowley, and also known as both Frater Perdurabo and The Great Beast, was an influential English occultist, astrologer, mystic and ceremonial magician, responsible for founding the religious philosophy of Thelema. He was also successful in various other...

, said of it in his book Magick Without Tears

Magick Without Tears

Magick Without Tears, a series of letters, was the last book written by English occultist Aleister Crowley , although it was not published until after his death. It was written in the mid-1940s and published in 1954 with a foreword by its editor, Karl Germer.-Summary:The book consists of 80 letters...

:

The Great Work is the uniting of opposites. It may mean the uniting of the soul with God, of the microcosm with the macrocosm, of the female with the male, of the ego with the non-ego."

For each individual this Great Work may take different forms. Crowley described his own personal Great Work in the introduction to Magick (Book 4)

Magick (Book 4)

Magick, Liber ABA, Book 4 is widely considered to be the magnum opus of 20th century occultist Aleister Crowley, the founder of Thelema...

:

In my third year at Cambridge, I devoted myself consciously to the Great Work, understanding thereby the Work of becoming a Spiritual Being, free from the constraints, accidents, and deceptions of material existence.

Within the system of the A∴A∴ magical Order the Great Work of the Probationer Grade is considered to be the pursuit of self-knowledge to, as Crowley said in The Confessions of Aleister Crowley

The Confessions of Aleister Crowley

The Confessions of Aleister Crowley : An Autohagiography, by Aleister Crowley , is a book written in six parts, the first two parts published in 1929. It is subtitled "An Autohagiography" which refers to the autobiography of a Saint, a title which Crowley would also have associated with the...

, "obtain the knowledge of the nature and powers of my own being." However, Crowley continues, the Great Work should also be something that is integrated into the daily life of all:

I insist that in private life men should not admit their passions to be an end, indulging them and so degrading themselves to the level of the other animals, or suppressing them and creating neuroses. I insist that every thought, word and deed should be consciously devoted to the service of the Great Work. 'Whatsoever ye do, whether ye eat or drink, do all to the glory of God'.

Although Crowley often discussed the idea of "succeeding" or "accomplishing" in the Great Work, he also recognized that the process is ongoing. From his Little Essays Toward Truth

Little Essays Toward Truth

Little Essays Toward Truth is a 1938 book written by the mystic Aleister Crowley . It consists of sixteen philosophical essays on various topics within the framework of the Qabalah and Crowley's religion of Thelema...

:

The Quest of the Holy Grail, the Search for the Stone of the Philosophers—by whatever name we choose to call the Great Work—is therefore endless. Success only opens up new avenues of brilliant possibility. Yea, verily, and Amen! the task is tireless and its joys without bounds; for the whole Universe, and all that in it is, what is it but the infinite playground of the Crowned and Conquering Child, of the insatiable, the innocent, the ever-rejoicing Heir of Space and Eternity, whose name is MAN?

The term also appears in the Benediction at the end of Crowley's Gnostic Mass

Liber XV, The Gnostic Mass

Aleister Crowley wrote The Gnostic Mass — technically called Liber XV or "Book 15" — in 1913 while travelling in Moscow, Russia. In many ways it is similar in structure to the Mass of the Eastern Orthodox Church. However, the comparison ends there, as Liber XV is a celebration of the principles of...

, where the Priest blesses the congregation with the words:

The LORD bring you to the accomplishment of your true Wills, the Great Work, the Summum Bonum, True Wisdom and Perfect Happiness.