Theophylact of Ohrid

By this parable it is declared that one must not boast of any attainment, not even of the fulfillment of all the commandments. For upon a servant lies the necessary obligation to carry out the orders of his master, yet the fulfillment of them should not be reckoned to him as a virtue. For if the servant does not do his work, he is worthy of blows; but when he has done it, let him be content that he has escaped blows, and should not for this necessarily demand payment. …

Commentary on Luke ↗

Augustine of Hippo

While His servants also are ministering, that is, preaching the Gospel, our Lord is eating and drinking the faith and confession of the Gentiles. It follows, And afterward thou shall eat and drink. As if He says, After that I have been delighted with the work of thy preaching, and refreshed myself with the choice food of thy compunction, then at length shalt thou go, and feast thyself everlastingly with the eternal banquet of wisdom.

Catena Aurea by Aquinas ↗

Bede

And gird yourself and serve me while I eat and drink. To gird oneself is to restrict one's humble mind from all wandering thoughts by which the steps of duties are usually impeded. For whoever girds their clothes does this to avoid being entangled to the point of stumbling while walking. To serve God is to confess that one is insignificant in everything and has no strength without His grace. For a minister takes his name from a lower status, that is, subjection, just as a master takes his name from a higher status. …

On the Gospel of Luke ↗

Bonaventure

Whence he adds: And will he not say: Make ready what I may sup on, and gird yourself, and serve me until I eat and drink, namely through the groaning of interior compunction, in which each one prepares the banquet: Sirach 18: "Before prayer prepare your soul, and be not as a man who tempts God." He girds himself, by restraining the wanderings of the mind: 1 Peter 1: "Having the loins of your mind girt up" etc. …

Commentary on Luke, Chapter 17 ↗