William Burkitt on Matthew 18:21

Here St. Peter puts a question to our Saviour, how often Christians should forgive offences to their brethren professing repentance: Christ answers that there should be no end of our mutually forgiving one another, but we are to multiply our pardon as our brother manifests his repentance. Not that we are hereby obliged to take the frequent offender into our bosom, and to make him our intimate; but to lay aside all malice, and all thoughts and desires of revenge, and to stand ready to do him any office of love and friendship.

Learn, 1. That to fall often into the same offence against our brother, is a great aggravation of sin, so the multiplication of forgiveness is a great demonstration of a God-like temper in us. He that multiplies sin, doth like Satan, sin abundantly; and he that multiplies pardon, doth, like God, pardon abundantly.