Sin and salvation.
Evil is associated with matter, ignorance, formlessness, distortion. Consequently salvation is to slough off defilement rather than to receive forgiveness for offenses. Salvation comes as illumination dispelling ignorance, triumphing over the material. The Gospel is principally a means of men knowing the truth; the cosmic bodies receive the same instruction.
Judgment and resurrection were a constant source of difficulty for those who sought immortality in escape from the body. Resurrection, and the whole eschatological dimension associated with it, is noticeably missing from Gnostic schemes.
The Church and Christian life.
Some schools divided mankind into three according to the predominant element in their constitutions—the material (who were unsavable), the “psychic” who could receive some purification, and the spiritual, the elite capable of receiving the deep mysteries. Naturally the third class were the Gnostics, the mass of Christians forming the second class. The church becomes the club of the illuminated not the society of the redeemed. The view that the material is the seat of evil, leads to asceticism, celibacy and vegetarianism in some systems, and paradoxically to license in others, where “liberation” from matter meant its effects were inconsequential.
Source: https://www.biblegateway.com/resources/encyclopedia-of-the-bible/Gnosticism