Some of the believers in the Corinthian church congregation were taking other believers in the congregation to civil (Roman) courts and filing lawsuits against them. The Apostle Paul does not tell us what they were about; he just says this is wrong.
He says that they should settle such matters within the church body. He supports his argument by saying, “Or do you not know that the saints (Christians) will judge the world?” (probably during the 1000 year reign of Jesus Christ). Paul closes with this argument, “Is … there not among you (the whole congregation) one wise man who will be able to decide between his brethren…?” (verse 5)
I must admit that I personally have never been a member of any church which had any two members going to court against each other regarding a civil disagreement. Praise the Lord.