that no one should take advantage of and wrong a brother or sister in this matter; because the Lord is an avenger in all these things, as also we forewarned you and testified.
"Paul reminds the Thessalonians that he had already forewarned them about this matter of sexual vice. Compare Galatians 1:9. Evidently when the apostles of Christ once spoke, their teaching was not to be modified later to suit someone’s pleasure and convenience" (Fields 107). (Note: The author was probably referring to Galatians 5:19.)