Then came to Jesus … – Mark says that they saw the disciples of Jesus eating with unwashed hands.
Transgress the tradition of the elders – The world “elders” literally means “old men.” Here it means the “ancients,” or their “ancestors.” The “tradition of the elders” meant something handed down from one to another by memory; some precept or custom not commanded in the written law, but which scribes and Pharisees held themselves bound to observe.
They supposed that when Moses was on Mount Sinai two sets of laws were delivered to him: one, they said, was recorded, and is that contained in the Old Testament; the other was handed down from father to son, and kept uncorrupted to their day. They believed that Moses, before he died, delivered this law to Joshua; he to the Judges; they to the prophets; so that it was kept pure until it was recorded in the Talmuds. In these books these pretended laws are now contained. They are exceedingly numerous and very trifling. They are, however, regarded by the Jews as more important than either Moses or the prophets.
One point in which the Pharisees differed from the Sadducees was in holding to these traditions. It seems, however, that in the particular traditions mentioned here, all the Jews were united; for Mark adds Mar 7:3 that “the Pharisees and all the Jews, except they wash their hands oft, eat not, holding the tradition of the elders.” Mark has also added that this custom of washing extended not merely to their hands before eating, but in coming from the market; and also to cups, and pots, and brass vessels, and tables, Mar 7:3-4. They did this professedly for the sake of cleanliness. So far it was well. But they also made it a matter of superstition. They regarded external purity as of much more importance than the purity of the heart. They had many foolish rules about it respecting the quantity of water that was to be used, the way in which it should be applied, the number of times it should be changed, the number of those that might wash at a time, etc. Our Saviour did not think it proper to regard these rules, and this was the reason why they “found fault” with him.
Link Collected : https://www.sacred-texts.com/bib/cmt/barnes/mat015.htm