Adam Clarke on 1 Thessalonians 4:6

That no man go beyond and defraud his brother - That no man should by any means endeavor to corrupt the wife of another, or to alienate her affections or fidelity from her husband; this I believe to be the apostle's meaning, though some understand it of covetousness, overreaching, tricking, cheating, and cozenage in general.

The Lord is the avenger of all such - He takes up the cause of the injured husband wherever the case has not been detected by man, and all such vices he will signally punish. Every species of uncleanness was practised among the heathens, nor were they reputed as vices. Their gods, their emperors, their philosophers, and their great men in general, gave them examples of every species of impurity; and they had no system of ethics which forbade these abominations. The Christian religion not only discountenances these things, but forbids them on the most awful penalties; therefore wherever Christianity prevails, these vices, if practised at all, are obliged to seek the deepest gloom of midnight to cover them from the eyes of men. On this account they are comparatively rare, even among the mere professors of Christianity; they exist, but do not flourish.