Gnosticism

The book says the Gnostics were a heretical Christian sect that had some scrolls that were later discovered. The main difference between the Gnostics and the Christian church was the Gnostic belief that, although God created the universe, a demiurge (a lower god) created the Earth and basically screwed things up badly when that was done.

They also believed that salvation was through the action of humans and not through the death of Jesus. It is the principle that true knowledge of ones self, not faith, is what saves a Gnostic.

The Gospel of Thomas, a book of 114 sayings, is one of their writings.

The demiurge asked for four powers: foreknowledge, eternal life, truth and incorruptibility.

There were 12 aeons created and Sophia Sophia is known as the Goddess of Wisdom. The book also describes a little about Adam and Eve and discusses the Gospel of Judas. The book also lists online resources and further reading suggestions.

The Everything Gnostic Gospels Book

This is an excellent, very through book on the Gnostic Gospels. It goes into an explanation of just what Gnosticism is, what the mythology of it holds, what kinds of writings there are, around when they were written and the war the Church waged against Gnosticism and everyone associated with it.

It also examines the concept that Gnosticism involves knowledge and self-awareness while traditional Christianity involves accepting the rules the churches lay down and accepting everything associated with Jesus. Gnosticism also accepts female involvement in leadership positions while Christianity in some areas is just beginning to accept that and in other areas still refuses women the right to be leaders.

In Christianity salvation comes from accepting the words of Jesus while in Gnosticism salvation comes from self-knowledge.

Other things discussed in the book include:

How original manuscripts often have words or entire sections missing.
Apocalyptic thinking
Polytheism
Mithraism
Zoroastrian
Types of Palestinian Jews
Heresies
Aeons
Archons
Demiurge
Dualism
The downgrading of the importance of Mary Magdalene
What is a Creed?
The immortality of the soul.
Adam and Eve
Baptism, the Bridal Chamber, Holy Eucharist, Redemption
The Q source
The Council of Nicaea and the banning of Gnostic writing
Who wrote which Gospel of the Bible
Redaction

There's a lot more besides those topics and there is also a glossary, Web resources and text resources.If you want one single book to learn about Gnosticism then this is the one.