This letter from the Elder is short and comes to the point quickly; the point being that we must not allow the poison of false teaching to infect our lives, our home, or the local fellowship of believers. He had already seen the damage done by the false doctrines of those denying that Jesus Christ had come in the flesh, and he was determined to do all he could to protect other churches and Christian fellowships from falling prey to these charlatans who were spreading deception and error. So being perhaps the last living apostle at that time, John stepped-up and stepped-in to send a warning to the church.
