This is a book I will keep as a reference.
The Gnostics were distinguished from other early Christians in their emphasis on gnosis, the Greek word for knowledge rather than faith. According to the Gnostics, it is gnosis itself that saves, redeems, and provides liberation. The Gnostics saw Jesus as a saviour and redeemer, but their Jesus saved and redeemed by bringing knowledge of the universe and Man’s place within it.
Gnosis is a direct kind of knowledge and might be translated as ‘acquaintance’ or ‘recognition’. True gnosis is a direct knowledge of the Self and the truth about the universe.
The Gnostics first appeared in the first centuries AD in the eastern Mediterranean. At the peak of their activity there were many different groups called Marcosians, Ophites, Cainites, Naasenes, and Carpocratians by the Church Fathers but really they were mainly Sethians and Valentinians. The author traces the line of Gnostics through to the Cathars and Paulicians and Bogomils a thousand years later and to the Mandaeans of modern-day Iraq.
Other spiritual systems have Gnostic qualities for instance Mahayana Buddhism, Kabbalah, and Neoplatonism.