Theophylact of Ohrid

There was a sacred treasury, contributed by the God-loving, which was used for repairs and restorations in the temple, and in general for the adornment of the temple and for the sustenance of the poor. But in recent times the priests converted even this treasury to commercial dealings, dividing it among themselves, rather than using it for the purpose for which it was originally designated.

Commentary on Luke ↗

Hegemonius

For here I perceive that Jesus also looks on willingly at the gifts of the rich men, when they are put into the treasury. All too little, at the same time, is it if gifts are cast into the treasury by the rich alone; and so there are the two mites of the poor widow which are also received with gladness; and in that offering verily something is exhibited that goes beyond what Moses prescribed on the subject of the receipt of moneys. For he received gifts from those who had; but Jesus receives them even from those who have not.

The Disputation With Manes 42 ↗

Ambrose of Milan

While [Jesus] stood in the temple, he also gave the verdict of which we are speaking. In the following verses, you have: "Jesus spoke these words in the treasury while teaching in the temple. And no one seized him." What is the treasury? It is the contribution of the faithful, the bank of the poor, and the refuge of the needy. Christ sat near this and, according to Luke, gave the opinion that the two mites of the widow were preferable to the gifts of the rich. …

Letters To Laymen 84 ↗

Bede

But looking up, He saw the rich putting their offerings into the treasury. Because in the Greek language, φυλάσσειν means to guard, and gaza in the Persian language means riches, the treasury was called the place where riches were kept. It was a chest with a hole on top, placed near the altar to the right of those entering the house of the Lord, into which the priests who guarded the doors put all the money brought to the temple of the Lord and its upkeep. Read the words of the days. …

On the Gospel of Luke ↗

Bonaventure

And looking up, he saw, etc. After he instructed the disciples toward caution against evils, here secondly he instructs them toward the choice of better things, and this by the example of a poor little widow, offering her entire livelihood, who is preferred above the others, who gave only a part. In this part, therefore, he proceeds in this order. For here is introduced the gift of the wealthy multitude, the offering of the poor little widow, the praise of the offering made by the widow, and the assignment of the reason and cause. …

Commentary on Luke, Chapter 21 ↗