Peter was aware of the devil's attempts to deceive believers. That is why he said that the devil goes around like a roaring lion seeking whom he may devour (1 Peter 5:8). In reality, the devil deceived Arius, who was a church elder and a believer. The ones who started the Gnostic movement were believers who were deceived. The deception comes when believer step away from the fellowship of other believers who may have been able to give correction. There is safety in a fellowship. Joseph Smith walked away from the Church and then got deceived, and everyone knows the outcome of that. A guy called Russell lost confidence in his church, walked away from it, and ended up getting deceived and started his own religion. Every pseudo-christian cult started with someone who moved away from the safety of a good fellowship, became isolated and then was picked off by the devil. In the Atlantic battle in World War two, ship were relatively safe in the convoy, but when a ship slowed down for whatever reason and dropped back and became isolated, it became an easy target for the German uboats. The scripture says that there is safety in the multitude of counsellors, not that these ones control us but that there is a safety in being able to check our views and opinions with others who might have a different perception of things.
