It should be noted, that when He spoke of fasting, alms, and other spiritual virtues, He did not bring in the comparison of Angels, but only here where He speaks of the ceasing of marriage. For as all acts of the flesh are primal acts, but this of lust especially so; so all the virtues are angelic acts, but especially chastity, by which our nature is bound to the other virtues.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).