Hence it seems to me more correct to account the father of the demoniac unbelieving, because he also casts reproach upon the holy Apostles, saying that they could not subdue the evil spirits. But it were better to have sought favour from God by honouring Him, for He has respect to them that fear Him. But he who says that those are weak with respect to their power over evil spirits, who have obtained that power from Christ, calumniates rather the grace than those who are adorned with that grace in whom Christ works. Christ is therefore offended with the accusation of the saints, to whom was entrusted the word of holy preaching. Wherefore the Lord rebukes him and those like-minded with him, saying, O faithless and perverse generation. As if He said, Because of your unbelief the grace has not received its accomplishment.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).
Also cites: ubi sup.