See Barnes "Mt 18:5, See Barnes "Mt 18:21, See Barnes "Mt 18:22".

Trespass against thee. Sin against thee, or does anything that gives you an offence or does you an injury.

Rebuke. Reprove. Go and tell him his fault, and seek an explanation. Acquaint him with what has been the effect of his conduct, and the state of your feelings, that he may acknowledge his error and repent.

{b} "rebuke him" Le 19:17