Bede the Venerable — as excerpted in the Catena Aurea on Mark 9:43-50

“(ubi sup.) Because the Lord had taught us not to offend those who believe on Him, He now as next in order warns us how much we should beware of those who offend us, that is, who by their words or conduct strive to drag us into the perdition of sin; wherefore He says, And if thy hand offend thee, cut it off.”