Here is a simple-to-understand difference.
What is Christian Gnosticism? How does modern Gnosticism compare with first century Gnosticism?
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Two main points:
First, it espouses a dualism regarding spirit and matter. Gnostics assert that matter is inherently evil and spirit is good. As a result of this presupposition, Gnostics believe anything done in the body, even the grossest sin, has no meaning because real life exists in the spirit realm only.
Second, Gnostics claim to possess an elevated knowledge, a “higher truth” known only to a certain few. Gnosticism comes from the Greek word gnosis which means “to know.” Gnostics claim to possess a higher knowledge, not from the Bible, but acquired on some mystical higher plane of existence. Gnostics see themselves as a privileged class elevated above everybody else by their higher, deeper knowledge of God.