That no man transgress and wrong his brother in any matter: because the Lord is the avenger of all such, as we also have forewarned you and testified.
All Commentaries on 1 Thessalonians 4:6 Go To 1 Thessalonians 4
John Chrysostom
AD 407
To each man God has assigned a wife. He has set boundaries on nature and limits sexual intercourse to one person only. Therefore, intercourse with another is transgression, and taking more than belongs to one, and robbery. Or rather it is more cruel than any robbery; for we grieve less when robbed of our riches than when our marriage is invaded. Do you call him a brother and yet wrong him, and that in things which are unlawful? … Paul does not mean by the use of the word brother that we are free to sleep with the wife of an unbeliever. Paul shows God will avenge and punish such an act, not to avenge the unbeliever but to avenge himself. Why? You have insulted God. He himself called you, and you in turn have insulted him. Whether you sleep with the empress or your married handmaid, it makes no difference. The crime is the same. Why? Because he does not avenge the injured persons but himself.