17 And his disciples remembered, that it was written: The zeal of thy house hath eaten me up.
Chrysostom: Why did Christ use such violence? He was about to heal on the Sabbath day, and to do many things which appeared to them transgressions of the Law. That He might not appear therefore to be acting contrary to God, He did this at His own peril; and thus gave them to understand, that He who exposed Himself to such peril to defend the decency of the house, did not despise the Lord of that house. For the same reason, to show His agreement with God, He said not, the Holy house, but, My Father’s house. It follows, And His disciples remembered what was written; The zeal of your house has eaten me up.
Alcuin: Zeal, taken in a good sense, is a certain fervor of the Spirit, by which the mind, all human fears forgotten, is stirred up to the defense of the truth.
Augustine: He then is eaten up with zeal for God’s house, who desires to correct all that he sees wrong there; and, if he cannot correct, endures and mourns. In thine house thou busiest thyself to prevent matters going wrong; in the house of God, where salvation is offered, oughtest thou to be indifferent?
18 The Jews, therefore, answered, and said to him: What sign dost thou shew unto us, seeing thou dost these things?
Chrysostom: Were signs necessary for His putting a stop to evil practices? Was not the having such zeal for the house of God, the greatest sign of His virtue? . . . This dilemma, they thought, would oblige Him either to work miracles, or give up His present course. But He refuses to give them the sign, as He did on a like occasion, when He answers, An evil and adulterous generation seeks after a sign, and there shall no sign be given it, but the sign of Jonas the prophet. [Matt 12:39]
Scripture from the Douay-Rheims Bible. Commentary from St. Thomas Aquinas, Catena Aurea, Vol. IV (London: Rivington, 1845).