From the Holy Gospel According to St. John (13:14,15 KJV):
If I then, your LORD and MASTER, have washed your feet; ye also ought to wash one another's feet. For I have given you an example, that ye should do as I have done to you.
In washing the feet of disciples who were already washed and clean, the LORD instituted a sign, to the end that, ... we might know that we are not exempt from sin, which HE thereafter washes away by interceding for us. ... What connection, then, can such an understanding of the passage have with that which HE afterwards gave HIMSELF, when HE explained the reason of HIS act in the words, "If I then, your LORD and MASTER, have washed your feet, ye also ought to wash one another's feet. For I have given you an example, that ye should do as I have done to you"? ... Let us listen to Apostle James, who states this precept with greatest clearness when he says, "Confess your faults one to another, and pray one for another." For of this also the LORD gave us the example. For if HE WHO neither has, nor had, nor will have any sin, prays for our sins, how much more ought we to pray for one another's in turn! And if HE forgives us, WHOM we have nothing to forgive, how much more ought we, who are unable to live here without sin, forgive one another! --Blessed Augustine