Cyril of Alexandria

Now our Lord might also have used other words to admonish the foolish Pharisee, but he seizes the opportunity and framed his reproof from the things that were ready before him. At the hour, namely, of meals He takes for His example the cup and the platter, pointing out that it became the sincere servants of God to be washed and clean, not only from bodily impurity, but also from that which lies concealed within the power of the soul, just as any of the vessels which are used for the table ought to be free from all inward defilement.

Catena Aurea by Aquinas ↗

Theophylact of Ohrid

And since it was mealtime, He mentions the cup and the dish and, drawing His testimony from what lay before their eyes, persuades the Pharisee that just as there is no benefit if a cup is clean on the outside but filled with all manner of filth on the inside, so too there is no benefit if, while the body is washed, the soul is filled with all manner of impurity, such as "greed and wickedness." The Lord alluded to two dominant passions of the Jews: by the word "greed" — to covetousness, and by the word "wickedness" — to envy and the …

Commentary on Luke ↗

Ambrose of Milan

Now mark that our bodies are signified by the mention of earthly and fragile things, which when let fall a short distance are broken to pieces, and those things which the mind meditates within, it easily expresses through the senses and actions of the body, just as those things which the cup contains within make a glitter without. Hence also hereafter, by the word cup doubtless the passion of the body is spoken of. You perceive then, that not the outside of the cup and platter defiles us, but the inner parts. …

Catena Aurea by Aquinas ↗

Bede

And the Lord said to him: Now you Pharisees clean the outside of the cup and of the dish, but inside you are full of greed and wickedness. And Mark indeed reports that they are accustomed to observe the washing of cups and pots, couches, and vessels of bronze, but under the guise of such vessels, they themselves are accused of the pretense of hypocrisy, because they show one thing to men outwardly, and do another thing at home, having the form of godliness outwardly, but inwardly they are deformed by the filth of vices. …

On the Gospel of Luke ↗

Bonaventure

Second, as regards the severity of the rebuke on the part of the Master, he adds: And the Lord said to him: Now you Pharisees make clean the outside of the cup and of the dish. The cup is a vessel for drinking, the dish for eating; and these vessels the Pharisees and Jews especially cleansed, because they thought themselves defiled by the uncleanness of vessels. …

Commentary on Luke, Chapter 11 ↗