When Jesus looked up he saw some wealthy people putting their offerings into the treasury and he noticed a poor widow putting in two small coins. He said, “I tell you truly, this poor widow put in more than all the rest; for those others have all made offerings from their surplus wealth, but she, from her poverty, has offered her whole livelihood.”
Our Lord having rebuked the covetousness of the Scribes who devoured widows' houses, commends the almsgiving of a widow; as it is said, "And he looked up, and saw the rich men casting into the treasury, &c."
Now there was a chest with an opening at the top placed near the altar, on the right hand of those entering the house of God, into which the Priests cast all the money, which was given for the Lord's temple. But our Lord as He overthrows those who trade in His house, so also He remarks those who bring gifts, giving praise to the deserving, but condemning the bad. Hence it follows, "And he saw also a certain poor widow casting in there two small coins."
She offered two small coins, which she had earned for her daily living, or what she daily begs for at the hands of others she gives to God, showing that her poverty is fruitful to her. Therefore does she surpass the others, and by a just award receives a crown from God; as it follows, "Of a truth I say to you, that this poor widow has cast in more, &c."
For whatever we offer with the whole heart is well pleasing to God, who has respect to the heart, not the substance, nor does He weigh the amount of that which is given in sacrifice, but the percentage of the total which it is taken as it follows, "For all these have cast in of their abundance, but she all that she had."
In all cases the will is needed, a right disposition, and a love towards God. If we do all things like this, though having little we give little, God will not turn away His face, but will receive it as great and admirable: for He regards the will, not the gifts: and if He see that to be great, He assigns His decrees and judges accordingly, and makes them partakers of His everlasting reward.
Catena Aurea (St. Thomas Aquinas)
On the Gospel of Luke (St. Bede the Venerable)
Sermon 138, Commentary on Luke (St. Cyril of Alexandria)
Homily 1 on Hebrews (St. John Chrysostom)