I don't know if you mean gnosticism as in Prue-Chrisitan origins, or *agnosticism* as in skeptical whether or not God exists. If you meant to spell it that way than some people don't know what you mean.
The Gnostics were among the first groups to put forth false doctrines about Jesus Christ. They knew many things about Him, but they denied that He was the Son of God, saying that when He was baptized by John the Baptist, the Holy Spirit came on Him, but left Him sometime before He died on the cross. They also said He never really came in the flesh, that He didn't rise from the dead, and many other things. All this was to subvert the message of the Gospel that the true apostles had. The Gnostics were false teachers and false prophets, trying to stop the Christian church from spreading.
false teaching and early Christian heresy based on acquiring secret "knowledge" (Greek "nosies") in order to reach enlightenment and salvation on ones own power and ability; rejects salvation purchased by the merits of Jesus Christ.
The Gnostic Gospels are the only gospels that have not been corrupted by man.
http://www.religioustolerance.org/gnostic.htm
The church feared the Gnostic's because they taught that Jesus spoke of enlightenment, not hell.
As you can see, the church preferred a Christianity that was not about knowledge or enlightenment but was instead about fear and dogma.
A belief that salvation is achieved through relational and experiential knowledge. In the words of The contemporary Gnostic Apostolic Church, humanity needs to be awakened and brought "to a realization of his true nature. Mankind is moving towards the Omega Point, the Great day when all must graduate or fall. This day is also the Day of Judgment in that only those who have entered the Path of Transfiguration and are being reborn can return to the Treasury of Light."
Gnostics believed that the old testament god was an evil cruel tyrannical sadist... basically a cruel evil authority figure.
They believed that the only escape from this evil tyrant was through nosies or knowledge which they attained through the forbidden fruit, the manna from heaven, the bread of life, mushroom Jesus.
The stories in the bible are pianistic tales of astronomy, astrology, and psychedelic enlightenment written by gnostic types and the Essenes, based upon the teachings of the ancient Egyptian and Greek mystery schools. The Church stole these stories, persecuted these people, and have pushing this phone junk called Christianity ever since... the opiate of the masses... the church itself is the Antichrist of the bible.
It is a belief system that basically states that the flesh is evil and the eternal spirit is good. There are two divergent philosophies, one says that to subdue or punish the flesh to keep it pure. The other says the evil the flesh does can't touch the spirit so one can do anything they want. There are many gnostic religions still around, with some study, these groups are readily apparent.
gnosticism is a the dualistic belief. they believe in two gods: Jesus( who they believe is only god, not man) and the god of the old testament. Jesus is the "good" god in this dualistic relationship and the old testament god is the "bad" god.
Gnosticism is a belief that God allows you to know God through a form of communication that is spiritually mental. You are given nosies or knowledge of God directly from the source. Sometimes meditation, self denial and even self inflicted pain brings on this Gnosis.
This means of course that the written word is super ceded by personal experience. The early Gnostic's were heretics that were pushed out of the early Church of Rome as it was becoming catholic (universal). Gnosticism is gaining popularity again in some places.
Perhaps they are right, at least for themselves. It must be a very strong and personal experience. Personal experiences of a spiritual nature are always difficult to ignore.
Paul
Look up stuff on the disciple James (The one that is the Brother of Jesus).
The super short version is that Gnostics represent the second major break in Christianity (the first being whether you needed to be a Jew or not).
The Gnostics felt that spiritual betterment came through self improvement, internal reflection, and making oneself closer to God. The larger church felt the only way to God was through Jesus and later the defined books of the bible.
Also they had better weapons and government backing, and killed most of the Gnostic's, so you can tell which side 'won'.
Leading to the current slam job they telling people about the Gnostic teachings.
This is the best collection of answers I've seen to this question yet. Awareness is growing, slowly, but growing. Recent discoveries in archeology confirm much of what the Gnostics taught. To understand what the Gnostics thought (and still think) of regular Christianity, Catholic and Protestant, just read the "Apocalypse of Peter." Here's a link to the text of this threatening gospel that was left out of the Bible.
http://www.webcom.com/gnosis/naghamm/apopet.html
If you aren't interested in reading it let me quote a couple of high points.
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"And there shall be others of those who are outside our number who name themselves bishop and also deacons, as if they have received their authority from God. They bend themselves under the judgment of the leaders. Those people are dry canals."
But I said " I am afraid because of what you have told me, that indeed little (ones) are, in our view, the counterfeit ones, indeed, that there are multitudes that will mislead other multitudes of living ones, and destroy them among themselves. And when they speak your name they will be believed."
The Savior said, "For a time determined for them in proportion to their error they will rule over the little ones. And after the completion of the error, the never-aging one of the immortal understanding shall become young, and they (the little ones) shall rule over those who are their rulers. The root of their error he shall pluck out, and he shall put it to shame so that it shall be manifest in all the impudence which it has assumed to itself. And such ones shall become unchangeable, O Peter."
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This was where Yeshua predicted the rise of modern Christianity with all its error.
No wonder this book was left out and declared "dangerous."