2:19 They went out from us. Paul too warns against false teachers who will arise from among the believers (Acts 20:29–31). As in the case of Simon the sorcerer (Acts 8:9–24), visible membership in the church does not guarantee salvation. Inward apathy or hostility to the gospel may be masked by outward conformity. The false teachers revealed their hostility not just by leaving, but by the way they left. Because they went out to oppose the word of the gospel, their departure was as much a renunciation of the church and its message as was Judas’s departure from the Last Supper (John 13:30).