8 These men, however, deceive the people by the very Scriptures, that they may receive honors and praises at their hand, and that men may not turn to the truth. But in that they deceive, by the very Scriptures, the people of whom they seek honors, they do in fact sell oxen: they sell sheep too; that is, the common people themselves. And to whom do they sell them, but to the devil? For if the Church be Christ's sole and only one, who is it that carries off whatever is cut away from it, but that lion that roars and goes about, “seeking whom he may devour?” Woe to them that are cut off from the Church! As for her, she will remain entire. “For the Lord knows them that are His.” These, however, so far as they can, sell oxen and sheep, they sell doves too: let them guard against the scourge of their own sins. But when they suffer some such things for these their iniquities, let them acknowledge that the Lord has made a scourge of small cords, and is admonishing them to change themselves and be no longer traffickers: for if they will not change, they shall at the end hear it said, “Bind ye these men's hands and feet, and cast them forth into outer darkness.”
9. “Then the disciples remembered that it was written, The zeal of Your house has eaten me up:” because by this zeal of God's house, the Lord cast these men out of the temple. Brethren, let every Christian among the members of Christ be eaten up with zeal of God's house. Who is eaten up with zeal of God's house? He who exerts himself to have all that he may happen to see wrong there corrected, desires it to be mended, does not rest idle: who if he cannot mend it, endures it, laments it. The grain is not shaken out on the threshing-floor that it may enter the barn when the chaff shall have been separated. If you are a grain, be not shaken out from the floor before the putting into the granary; lest you be picked up by the birds before you be gathered into the granary. For the birds of heaven, the powers of the air, are waiting to snatch up something off the threshing-floor, and they can snatch up only what has been shaken out of it. Therefore, let the zeal of God's house eat you up: let the zeal of God's house eat up every Christian, zeal of that house of God of which he is a member. For your own house is not more important than that wherein you have everlasting rest. You go into your own house for temporal rest, you enter God's house for everlasting rest. If, then, you busy yourself to see that nothing wrong be done in your own house, is it fit that you suffer, so far as you can help, if you should chance to see anything wrong in the house of God, where salvation is set before you, and rest without end? For example, do you see a brother rushing to the theatre? Stop him, warn him, make him sorry, if the zeal of God's house does eat you up. Do you see others running and desiring to get drunk, and that, too, in holy places, which is not decent to be done in any place? Stop those whom you can, restrain whom you can, frighten whom you can, allure gently whom you can, do not, however, rest silent. Is it a friend? Let him be admonished gently. Is it a wife? Let her be bridled with the utmost rigor. Is it a maid-servant? Let her be curbed even with blows. Do whatever you can for the part you bear, and so you fulfill. “The zeal of Your house has eaten me up.” But if you will be cold, languid, having regard only to yourself, and as if yourself were enough to you, and saying in your heart, What have I to do with looking after other men's sins? Enough for me is the care of my own soul: this let me keep undefiled for God—come, does there not recur to your mind the case of that servant who hid his talent and would not lay it out? Was he accused because he lost it, and not because he kept it without profit? So hear ye then, my brethren, that you may not rest idle. I am about to give you counsel: may He who is within give it; for though it be through me, it is He that gives it. You know what to do, each one of you, in his own house, with his friend, his tenant, his client, with greater, with less: as God grants an entrance, as He opens a door for His word, do not cease to win for Christ; because you were won by Christ.
10. “The Jews said unto Him, What sign do you show unto us, seeing that you do these things?” And the Lord answered, “Destroy this temple, and in three days I will raise it up. Then said the Jews, Forty and six years was this temple in building, and do you say, In three days I will rear it up?” Flesh they were, fleshly things they minded; but He was speaking spiritually. But who could understand of what temple He spoke? But yet we have not far to seek; He has discovered it to us through the evangelist, he has told us of what temple He said it. “But He spoke,” says the evangelist, “of the temple of His body.” And it is manifest that, being slain, the Lord did rise again after three days. This is known to us all now: and if from the Jews it is concealed, it is because they stand without; yet to us it is open, because we know in whom we believe. The destroying and rearing again of that temple, we are about to celebrate in its yearly solemnity: for which we exhort you to prepare yourselves, such of you as are catechumens that you may receive grace; even now is the time, even now let that be purposed which may then come to the birth. Now, that thing we know.
Source: Tractates on the Gospel of John (New Advent)