“And everything is according to the multitude of the deed” (Avot ).
Lofty levels of development are not reached through the great size of a deed but rather through the great number of deeds. Repeated performance of good deeds gives one a strong hold on the level he aspires to, something that a single major performance alone cannot provide. The classic example is one who gives a thousand gold coins to one person in need but nothing to another. He will not develop the characteristic of generosity as well as one who gives one coin a thousand times. The latter’s repeated acts of generosity gave him a strong hold on this trait, while the former experienced a great single inspiration, which not reinforced and therefore evaporated.
The same is true in regard to the Torah’s reward for good deeds. The reward of one who ransomed one captive with a hundred coins or gave a poor man a hundred coins is not as great as that of one who ransomed ten captives or gave ten poor people ten coins each.