It was a fundamental principle of the Pharisees that by the side of the written law there was an oral law, to complete and to explain the written law. It was and is believed that God had given to Moses all explanations necessary for their application, with the order to transmit them by word of mouth. Moses, it is believed, received the (oral) law from Sinai, and delivered it to Joshua, and Joshua to the elders, and the elders to the prophets and the prophets to the men of the Great Synagogue. In the second century, first major written collection of the Jewish oral traditions known as the Mishna was made available. A second section of the Talmud, known as the Gemara is a rabbinical commentary on the Mishnah.
Then came together unto him the Pharisees, and certain of the scribes, which came from Jerusalem. And when they saw some of his disciples eat bread with defiled, that is to say, with unwashen, hands, they found fault. For the Pharisees, and all the Jews, except they wash their hands oft, eat not, holding the tradition of the elders. And when they come from the market, except they wash, they eat not. And many other things there be, which they have received to hold, as the washing of cups, and pots, brasen vessels, and of tables. Then the Pharisees and scribes asked him, Why walk not thy disciples according to the tradition of the elders, but eat bread with unwashen hands? He answered and said unto them, Well hath Esaias prophesied of you hypocrites, as it is written, This people honoureth me with their lips, but their heart is far from me. Howbeit in vain do they worship me, teaching for doctrines the commandments of men. For laying aside the commandment of God, ye hold the tradition of men, as the washing of pots and cups: and many other such like things ye do. And he said unto them, Full well ye reject the commandment of God, that ye may keep your own tradition.(Mar 7:1-9)
These verses do not appear in Matthew’s parallel account. They explain Pharisaic tradition for those unfamiliar with it such as Mark’s original Gentile readers. In Jesus’ day the Jews communicated the traditions of the elders orally from generation to generation. About A.D. 200 the rabbis completed compiling these into the Mishnah, which became the basis for the Talmud (ca. A.D. 425). The Pharisees customarily washed themselves after visiting the marketplace to rid themselves of the defilement that contact with Gentiles produced. Most Jews regarded breaking these traditions as sin. Mark 7:3-4 Thomas Constable
“History reveals that the Jewish religious leaders came to honor their traditions far above the Word of God. Rabbi Eleazer said, ‘He who expounds the Scriptures in opposition to the tradition has no share in the world to come.’ The Mishna, a collection of Jewish traditions in the Talmud, records, ‘It is a greater offense to teach anything contrary to the voice of the Rabbis than to contradict Scripture itself.’ Warran Wiersbe quoted by Constable Mark 7:10-13