This section in Matthew’s Gospel is commonly called the “woes”, because it is a series of invectives against the Pharisees and the doctors of the Law (or “scribes’, as they were commonly called.).
The passage treated here plays on the Pharisee’s love for external cleanliness and propriety and his tolerance of all sorts of internal corruption – “robbery and self-indulgence, all kinds of filth, hypocrisy and crime…”
. Externally, every Jew was expected to observe the proprieties; and the Pharisees were obsessive about such cleanliness. But cleanliness of heart is more important than cleanliness of hands and feet.
The Pharisees and those like them loved to appear pure. Yet, their interior disposition was such as to contradict this pious façade altogether.