How the Early Church reacted to Church-Splitters and False Teachers

Church discipline is never an appealing topic, especially in nice British culture. Sometimes its necessary, but even then we can all too easily create a sacred/secular divide in the interests of niceness. The Early Church didn't have quite the same hangups about niceness that we do. They recognised schism (splitting the church) as a serious sin, and false teaching as a matter of eternal life and death for those who'd be led astray by it. And so they dealt quite firmly with schismatics (church-splitters) and heretics. Here's an example that tells us how the apostle John and his disciple Polycarp reacted to them:

‘Some also heard from him [Polycarp] that when John, the disciple of the Lord, went to the baths at Ephesus but discovered that Cerinthus was there, he rushed out of the bathhouse without bathing, exclaiming, “Let us flee, in case the bathhouse falls down, because Cerinthus, the enemy of the truth, is inside it.” On another occasion, Marcion met Polycarp and asked, “Do you know who I am?” Polycarp responded, “I know who you are: you the first-born of Satan!” These stories reveal the determination of the apostles and those who had learned from them not even to interact with those who corrupt the truth. This squares with what Paul instructs, “After a first and second admonition, have nothing more to do with anyone who causes divisions, since you know that such a person is perverted and sinful, being self-condemned” [Titus 3:10-11].’
(Irenaeus, Against Heresies, 3.3.4)