8 Who is the hireling that sees the wolf coming, and flees? He that seeks his own, not the things which are Jesus Christ's. He is one that does not venture plainly to rebuke an offender. Look, some one or other has sinned— grievously sinned; he ought to be rebuked, to be excommunicated: but once excommunicated, he will turn into an enemy, hatch plots, and do all the injury he can. At present, he who seeks his own, not the things that are Jesus Christ's, in order not to lose what he follows after, the advantages of human friendship, and incur the annoyances of human enmity, keeps quiet and does not administer rebuke.
See, the wolf has caught a sheep by the throat; the devil has enticed a believer into adultery: you hold your peace — you utter no reproof. O hireling, you have seen the wolf coming and hast fled! Perhaps he answers and says: See, I am here; I have not fled. You have fled, because you have been silent; you have been silent, because you have been afraid. The flight of the mind is fear. Thou stoodest with your body, you fled in your spirit, which was not the conduct of him who said, “Though I be absent in the flesh, yet am I with you in the spirit.” For how did he flee in spirit, who, though absent in the flesh, yet in his letters reproved the fornicators?
Our affections are the motions of our minds. Joy is expansion of the mind; sorrow, contraction of the mind; desire, a forward movement of the mind; and fear, the flight of the mind. For you are expanded in mind when you are glad; contracted in mind when you are in trouble; you move forward in mind when you have an earnest desire; and you flee in mind when you are afraid. This, then, is how the hireling is said to flee at the sight of the wolf. Why? “Because he cares not for the sheep.”
Why “cares he not for the sheep”? “Because he is an hireling.” What is that, “he is an hireling”? He seeks a temporal reward, and shall not dwell in the house for ever. There are still some things here to be inquired about and discussed with you, but it is not prudent to burden you. For we are ministering the Lord's food to our fellow-servants; we feed as sheep in the Lord's pastures, and are fed together. And just as we must not withhold what is needful, so our weak hearts are not to be overcharged with the abundance of provisions. Let it not then annoy your Charity that I do not take up today all that I think is still here to be discussed; but the same lesson will, in the Lord's name, be read over to us again on the preaching days, and be, with His help, more carefully considered.
Source: Tractates on the Gospel of John (New Advent)