One of the effects of the body of Christ being united together into a compactly joined organization is that believers will be permanently disconnected from unbelievers in eternity. For this reason, Paul told the Corinthians, “Do not be unequally yoked together with unbelievers. For what fellowship has righteousness with lawlessness? And what communion has light with darkness?…For you are the temple of the living God” (2 Corinthians 6:14, 16, NKJV). The phrase unequally yoked together has to do with a coupling that prevents two people from going in different directions. Paul contrasted righteousness and lawlessness and light with darkness in order to illustrate the impossibility of two completely different natures being able to happily coexist.
Although Paul’s instruction to not be unequally yoked with unbelievers is often interpreted in the context of marriage, it seems unlikely that he was referring to that kind of a relationship. The Greek term translated fellowship, metoche (met-okh-ay) refers to participation in the Lord’s supper (G3352) and the Greek term translated communion, koinonia (koy-nohn-ee’-ah) has to do with social intercourse between believers (G2842). Koinonia is derived from the word koinonos (koy-no-nos’) which means “a sharer that is associate” (G2844). The primary root word of koinonia and koinonos is sun (soon) which denotes union; that is by association companionship process or resemblance (G4862). The Greek word sun is often used to describe the companionship between Jesus and his disciples; Jesus was “with” his disciples (Mark 8:34).
Paul quoted two verses from the prophets Isaiah and Jeremiah about the restoration of Israel and Jerusalem to emphasize the importance of believers being separated from unbelievers. He said, “Come out from among them and be separate, says the Lord. Do not touch what is unclean, and I will receive you. I will be a Father to you and you shall be My sons and daughters, Says the Lord Almighty” (2 Corinthians 6:17-18). The Greek word Paul used that is translated separate, aphorizo (af-or-id’-zo) means literally “to mark off by boundaries or limits” (G873). Paul was probably thinking of the opposite of fellowship and communion when he instructed the Corinthians to be separate from unbelievers. Today we might say, don’t hang out with them or stay away from the places that unbelievers like to go.
One of the reasons believers and unbelievers don’t usually get along with each other is because they have different concepts of repentance. Paul compared godly sorrow with the sorrow of the world and said, “For godly sorrow produces repentance leading to salvation, not to be regretted; but the sorrow of the world produces death” (2 Corinthians 7:10, NKJV). What Paul was saying was the outcome of repentance is supposed to be salvation, but unbelievers don’t want to be saved. The thing that usually separates believers from unbelievers is that even though both of these groups of people feel sad when things aren’t going well for them, unbelievers aren’t willing to do anything about it. They are content living in sin.