Albert Barnes Commentary 1 Corinthians 6:8

"Nay, but ye yourselves do wrong, and defraud, and that [your] brethren." — 1 Corinthians 6:8 (ASV)

Nay, ye do wrong, etc. Instead of enduring wrong patiently and cheerfully, they were themselves guilty of injustice and fraud.

And that your brethren. Your fellow Christians. As if they had injured those of their own family—those to whom they ought to be attached by most tender ties.

The offense in such cases is aggravated, not because it is in itself any worse to injure a Christian than another person, but because it shows a deeper depravity when a person overcomes all the ties of kindness and love and injures those who are near to them, than when no such ties exist.

It is for this reason that parricide, infanticide, etc., are regarded everywhere as crimes of peculiar atrocity, because a child or a parent must have severed all the tenderest cords of virtue before it could be done.