Thomas Aquinas

Then he brings them to sound doctrine: you blind Pharisee, first make clean the inside of the cup and of the dish. All exterior purity is from interior purity, as it says above at 6:22: if your eye be single, your whole body shall be lightsome, etc. Therefore he teaches that one should cleanse the heart, and so the whole will be clean. Hence he says, you blind Pharisee, etc. Wisdom 2:21: their own malice blinded them. …

Commentary on Matthew ↗