4 What, then, is the charge given? Verily, verily, I say unto you, says the Truth who surely, though He had not said, Verily, I say, could not possibly lie. Yet [thereby] He impresses, inculcates His charge, arouses in a way the sleeping, makes them attentive, and would not be contemned. What does He say? “Verily, verily, I say unto you, that every one who commits sin is the servant of sin.” Miserable slavery! Men frequently, when they suffer under wicked masters, demand to get themselves sold, not seeking to be without a master, but at all events to change him.
What can the servant of sin do? To whom can he make his demand? To whom apply for redress? Of whom require himself to be sold? And then at times a man's slave, worn out by the commands of an unfeeling master, finds rest in flight. Whither can the servant of sin flee? Himself he carries with him wherever he flees. An evil conscience flees not from itself; it has no place to go to; it follows itself. Yea, he cannot withdraw from himself, for the sin he commits is within. He has committed sin to obtain some bodily pleasure.
The pleasure passes away; the sin remains. What delighted is gone; the sting has remained behind. Evil bondage! Sometimes men flee to the Church, and we generally permit them, uninstructed as they are— men, wishing to be rid of their master, who are unwilling to be rid of their sins. But sometimes also those subjected to an unlawful and wicked yoke flee for refuge to the Church; for, though free-born men, they are retained in bondage: and an appeal is made to the bishop. And unless he care to put forth every effort to save free-birth from oppression, he is accounted unmerciful.
Let us all flee to Christ, and appeal against sin to God as our deliverer. Let us seek to get ourselves sold, that we may be redeemed by His blood. For the Lord says, “You were sold for nought, and you shall be redeemed without money.” Without price, that is, of your own; because of mine. So says the Lord; for He Himself has paid the price, not in money, but His own blood. Otherwise we had remained both bondmen and indigent.
Source: Tractates on the Gospel of John (New Advent)