Theophylact of Ohrid

The Lord praises the widow more than all the rest, because she cast in all her substance out of her poverty. For two mites, it would seem, are insignificant, but for one who lived on alms they constituted her whole livelihood, for the widow was destitute. Thus the Lord bestows His reward, paying attention not to how much is given, but to how much remains. In the houses of the rich, who brought little and small offerings, far more remained, but her house was completely emptied, and nothing was left in it. …

Commentary on Luke ↗

Desert Fathers

A hermit said, 'One man eats a lot and is still hungry. Another eats a little and has had enough. The man who eats a lot and is still hungry has more merit than the man who eats the little that satisfies him.'

The Desert Fathers, Sayings of the Early Christian Monks ↗

Bede

For all these out of their abundance have cast into the gifts of God; but she out of her poverty has cast in all the livelihood that she had. The Jew casts into the gifts of God out of his abundance, who, presuming on his own righteousness, prays thus with himself: "God, I thank you that I am not like other men, extortioners, unjust, etc." (Luke 18). …

On the Gospel of Luke ↗

Bonaventure

Fourth, with respect to the assignment of the reason and cause, he subjoins: For all these out of their abundance have cast into the gifts of God: and they fulfilled that precept above in chapter 11: "But yet that which remains, give as alms"; by which it is commanded to give out of one's abundance, as John said above in chapter 3: "He who has two tunics, let him give one to him who has none." But she out of her want has cast in all the living that she had: and thus she fulfilled a counsel, because she reserved nothing for herself, …

Commentary on Luke, Chapter 21 ↗