We use the word to mean “wrong belief.” In the New Testament the Greek word hairesis could refer to a philosophical school of thought.
It could also refer to a splinter group, and that is how it is used in the New Testament where there was a danger of breaking up the unity of Christian belief and lifestyle.
Paul told the Corinthians that the purpose of “splinter groups” was so that believers could learn to recognize right belief (1 Cor. 11:19).
But the New Testament also used hairesis to mean false belief, as in 2 Peter 2:1: “There will be false teachers among you, who will secretly bring in destructive heresies, even denying the Lord who bought them, and bring on themselves swift destruction.”
Over the centuries Christians have persecuted—sometimes even executed—heretics. The New Testament, even though it emphasizes correct belief as well as correct behavior, does not condone harming heretics.
The worst punishment for false belief is exclusion from fellowship with Christians.