To “Matthew 18” someone isn’t exactly like beating them over the head with a Bible, but it’s kinda close. This term is about disciplinary action within a church.
Some Christianese terms have achieved circulation outside of the church. For example, many people who aren’t Christians are still familiar with the trendy slogan “What Would Jesus Do?” But there are other Christianese terms that are barely known outside of Christian circles because the terms deal with serious and somewhat private matters. Matthew-18 is one of those terms.
“Church discipline” is the technical term for the corrective or disciplinary action that is taken when somebody runs afoul of the rules in church and the church leaders get involved to try to resolve the issue. The Christianese term for one kind of disciplinary action is matthew-eighteen. This refers to when church leaders chastise someone in the church according to a method that is described by Jesus himself. Talk about getting your marching orders from the boss man himself!
Here are the relevant verses in Matthew 18. In this passage Jesus is talking to his disciples:
“If your brother sins against you, go and tell him his fault, between you and him alone. If he listens to you, you have gained your brother. But if he does not listen, take one or two others along with you, that every charge may be established by the evidence of two or three witnesses. If he refuses to listen to them, tell it to the church. And if he refuses to listen even to the church, let him be to you as a Gentile and a tax collector.” (Matthew 18:15-17)
Jesus offers three modes of communication, and he says to start with the first one and escalate level-by-level if the problem isn’t being resolved. In summary, the three levels are: (1) talk with the person one-on-one; (2) talk with the person with some witnesses present; (3) make it an official church-wide issue and have expulsion from the church be the final consequence.
It’s hard to develop an entire disciplinary strategy from just a few sentences, so not all churches practice the “Matthew 18” strategy, and of the churches that do try to implement it, there is a lot of variation in how each church does it.
Let’s face it. Getting into trouble with an organization you’re part of is usually a serious deal, and it’s not usually the kind of situation where you want to use slangy Christianese. Slang is inherently playful and a little tongue-in-cheek, and since church discipline is usually a serious, even sad state of affairs, you don’t hear “matthew-18” being used too often, at least not until after the situation has died down.