Ancient Greek Expositor

Because he receives the reward of his own good works, he is said to be set over ten cities. And some conceiving unworthily of these promises imagine that they themselves are preferred to magistracies and chief places in the earthly Jerusalem, which is built with precious stones, because they have had their conversation honest in Christ; so little do they purge their soul of all hankering after power and authority among men.

Catena Aurea by Aquinas ↗

Bede

And he said to him: Well done, good servant, because you have been faithful in a very little, you shall have authority over ten cities. The servant is faithful in a very little, who does not adulterate the word of God, but speaks in Christ as from God, in the presence of God (II Cor. II). For whatever we receive of gifts at present is in comparison to the future very little and small, for we know in part, and we prophesy in part. But when that which is perfect has come, that which is in part shall be done away (I Cor. XIII). …

On the Gospel of Luke ↗

Bonaventure

Second, with regard to the acceptance of the heavenly judgment, he adds: And he said to him: Well done, good servant, because you have been faithful in a little. And note that well done is sometimes mocking, according to that passage of the Psalm: "They said: Well done, well done, our eyes have seen it." Sometimes it is flattering; the Psalm: "Let them be turned back immediately in shame who say to me: Well done, well done"; and again: "Let them bear their confusion at once who say to me: Well done, well done"; because flattery must …

Commentary on Luke, Chapter 19 ↗