In both the canonical gospels and the Gospel of Thomas, several teachings link knowledge of Christ to salvation, this idea may have been the core around which Gnosticism was formed. We observe however that knowledge of Christ was not enough to attain salvation for the fallen angels (for example). Inclination of the will toward Christ, or at least toward virtue is required.
The Gnostics strayed more significantly in that they did not subscribe to the sacraments, they believed Christ to be simply a higher order semi-god, and they saw the material world as inherently evil.