The washing of the feet signifies the washing away of stains. You therefore wash the feet of your brother when, as far as lies in your power, you wash away his stains. And this you may do in three wavs :
(i) By forgiving the offences he has done to you. Forgiving one another, if any have a complaint against another : even as the Lord hath forgiven you, so do you also (Coloss. iii. 13).
(ii) By praying for the forgiveness of his sin, as St. James bids us, Pray for one another, that you may be saved (James v. 16). This way of washing, like the first, is open to all the faithful.
(iii) The third way is for prelates, who should wash by forgiving sins through the authority of the keys, according to the gospel, Receive ye the Holy Ghost ; whose sins you shall forgive, they are forgiven them (John xx. 23).
--St. Thomas Aquinas
