It is perseverance which is the glory, the perfection, and, as it were, the virtue of all the virtues. Now charity is also a virtue which is much praised - a virtue, indeed, which deserves much praise for it is the life and virtue of the other virtues - but the virtue of charity is patience, and the virtue of patience is perseverance. Charity without patience is not true charity but an imitation, and imitation charity flourishes in good times but collapses in adversity. Patience without perseverance is inconstant and feeble; it is born in adversity, but it weakens in the course of time, and with prolonged effort it succumbs. It is as if all the other virtues were running in a race, but that which takes the prize is the straight course of perseverance.
Tractate 4; CF 38:105