Cornelius a Lapide

Then said He unto them , O fools . ’Aronro/, rendered here in the Vulgate “ stulti,” but Gal. iii. 1., “ insensati.” With these keen words Christ as the Master rebukes the disciples for their ignorance and slowness to believe. For a teacher is allowed to stimulate his disciples by sharp reproof to the pursuit of higher or more accurate knowledge. See S. Matt v. 22. So our nature, frail and dull of understanding, needs some such stimulus to enable it to believe in spiritual things, and to keep itself steadfast in the hope of their realisation