Limits must be observed, especially on the sexual terrain. Going too far here means ruining marriages and provoking fierce reactions. Above all, let it be remembered that God’s eyes see what is happening in secret. Keep in mind that he reacts to that with judgment (Psalm 94:1–2). That can already happen in this life, as the apostle Paul writes in Romans 1:24–32, but it will surely happen when Jesus returns.
You know that we have already pointed this out to each other emphatically, Paul reminds his readers once again.
6 that no one transgress and wrong his brother in this matter, because the Lord is an avenger in all these things, as we told you beforehand and solemnly warned you.