Jesus said, “Woe to you, scribes and Pharisees, you hypocrites. You pay tithes of mint and dill and cummin, and have neglected the weightier things of the law: judgment and mercy and fidelity. But these you should have done, without neglecting the others. Blind guides, who strain out the gnat and swallow the camel!
“Woe to you, scribes and Pharisees, you hypocrites. You cleanse the outside of cup and dish, but inside they are full of plunder and self-indulgence. Blind Pharisee, cleanse first the inside of the cup, so that the outside also may be clean.”
The Lord had commanded, that for the maintenance of the Priests and Levites, whose portion was the Lord, tithes of every thing should be offered in the temple. Accordingly, the Pharisees (to dismiss mystical expositions) concerned themselves about this alone, that these trifling things should be paid in, but overlooked other weightier things. He charges them then with covetousness in exacting carefully the tithes of worthless herbs, while they neglected justice in their transactions of business, mercy to the poor, and faith toward God, which are weighty things. And because it was much less guilt to omit the tithing of herbs than a duty of benevolence, the Lord derides them, "You blind guides, which strain out a gnat, and swallow a camel."
But because it was possible that some, hearing the Lord speak thus, might thereupon neglect paying tithes of small things, He prudently adds, "These things ought you to have done, (i.e. justice, mercy, and faith,) and not to leave the others undone, (i.e. the tithing of mint, anise, and cummin.)" In these words the Lord shows that all the commandments of the Law, greatest and least, are to fulfilled. They also are refuted who give alms of the fruits of the earth, supposing that doing this they cannot sin, whereas their alms do them no good unless they are careful to keep themselves from sin.
In different words, but for the same reason as before, Jesus reproves the hypocrisy and dissimulation of the Pharisees, that they showed one face to men abroad, but wore another at home. He means not here, that their scrupulousness respecting the cup and the platter was of any importance, but that they affected it to pass off their sanctity upon men; which is clear from His adding, "but inwardly you are full of ravening and uncleanness." He therefore is reproving those who, pursuing an ostentation of useless scrupulosity, neglected the discharge of useful morality. For it is the inside of the cup that is used; if that be foul, what good is it to cleanse the outside? And therefore what is needed is purity of the inner conscience, that those things which are of the body may be cleansed.
Catena Aurea (St. Thomas Aquinas)
Commentariorum In Evangelium Matthaei (St. Jerome)
In Evangelium Matthaei Commentarius (St. Hilary of Poitiers)
St. Remigius of Auxerre