What business is it of mine to judge those outside the church? Are you not to judge those inside? 13 God will judge those outside. “Expel the wicked person from among you.” (I Corinthians 5:12-13)
According to this verse, Christians are not supposed to “judge” unbelievers who live outside the church. In this context, “judging” means use church discipline (excommunication) to dictate what actions are and are not acceptable. Christians should not try to manage the actions of unbelievers: unbelievers are living in rebellion against God, and any attempt to manage their actions ignores the fact that their hearts are far from God. True change only happens with the indwelling of the Holy Spirit, something that unbelievers do not have. Therefore, we ought to simply preach the gospel to unbelievers and tell them to repent, but we should not try to get them to change their actions through threats of ostracizing them.
However, we are required to judge other believers. Again, “judging” in this context does not mean that we can question their motives, since we are unable to see inside their heart. It is really their actions, not their thoughts that we are judging here. Some actions are so wicked that there is no justification for them: these are the actions that need to be “judged” by the church. Specifically, we need to “judge” so-called believers who are consistently sexually immoral, greedy, idolaters, slanderers, drunkards, or swindlers. We must not even ask these people over to lunch, since they bring shame to the name of Christ.