4 For what is a greater or a more worthy care of overseers, than to provide by diligent solicitude and wholesome medicine for cherishing and preserving the sheep? Since the Lord speaks, and says, “The diseased you have not strengthened, neither have you healed that which was sick, neither have you bound up that which was broken, neither have you brought again that which was driven away, neither have you sought that which was lost. And my sheep were scattered because there is no shepherd; and they became meat to all the beasts of the field, and none did search or seek after them.
Therefore thus says the Lord, Behold, I am against the shepherds, and I will require my flock at their hands, and cause them to cease from feeding the flock; neither shall they feed them any more: for I will deliver them from their mouth, and I will feed them with judgment.” Since therefore the Lord thus threatens such shepherds by whom the Lord's sheep are neglected and perish, what else ought we to do, dearest brother, than to exhibit full diligence in gathering together and restoring the sheep of Christ, and to apply the medicine of paternal affection to cure the wounds of the lapsed, since the Lord also in the Gospel warns, and says, “They that be whole need not a physician, but they that are sick?” For although we are many shepherds, yet we feed one flock, and ought to collect and cherish all the sheep which Christ by His blood and passion sought for; nor ought we to suffer our suppliant and mourning brethren to be cruelly despised and trodden down by the haughty presumption of some, since it is written, “But the man that is proud and boastful shall bring nothing at all to perfection, who has enlarged his soul as hell.” And the Lord, in His Gospel, blames and condemns men of that kind, saying, “You are they which justify yourselves before men, but God knows your hearts: for that which is highly esteemed among men is abomination in the sight Of God.” He says that those are execrable and detestable who please themselves, who, swelling and inflated, arrogantly assume anything to themselves. Since then Marcian has begun to be of these, and, allying himself with Novatian, has stood forth as the opponent of mercy and love, let him not pronounce sentence, but receive it; and let him not so act as if he himself were to judge of the college of priests, since he himself is judged by all the priests.
Source: The Epistles of Cyprian (New Advent)