Also in Windsor Park, Mistress Page is reminding Doctor Caius that Anne will be wearing green.
After Caius exits, Mistress Page comments to Mistress Ford that Falstaff is well deserving of the mockery he will receive that night. She adds …
Against such lewdsters and their lechery
Those that betray them do no treachery. (19-20)
An act of betrayal (or treachery) was usually considered to be a terrible sin. In Dante’s Divine Comedy sinners of treachery were placed in the ninth and deepest level of Hell. However, according to the wives, if the victim of that betrayal is a sinner, than the treachery is acceptable and even blameless.