Matthew 16:11,12 speak of the Leaven of the Rabbis. What is this?
11 How is it you do not understand that I did not speak to you concerning bread?—but to beware of the leaven of the Pharisees and Sadducees.” 12 Then they understood that He did not tell them to beware of the leaven of bread, but of the doctrine of the Pharisees and Sadducees.
As the verse clearly states, it is the doctrine of the Pharisees and the Sadducees. What doctrine would that be? Well here is an example of how Jesus dealt with the rabbinic oral tradition of ritually washing hands before eating (Matthew 15:1-9):
1 Then the scribes and Pharisees who were from Jerusalem came to Jesus, saying, 2 “Why do Your disciples transgress the tradition of the elders? For they do not wash their hands when they eat bread.”
3 He answered and said to them, “Why do you also transgress the commandment of God because of your tradition? 4 For God commanded, saying, ‘Honor your father and your mother’; and, ‘He who curses father or mother, let him be put to death.’ 5 But you say, ‘Whoever says to his father or mother, “Whatever profit you might have received from me is a gift to God”— 6 then he need not honor his father or mother.’ Thus you have made the commandment of God of no effect by your tradition. 7 Hypocrites! Well did Isaiah prophesy about you, saying:
8 ‘These people draw near to Me with their mouth,
And honor Me with their lips,
But their heart is far from Me.
9 And in vain they worship Me,
Teaching as doctrines the commandments of men.’ ”
Did the rabbis have the authority to create new laws?
Deuteronomy 4:2 clearly states that we should not add to nor take away any of God’s commandments:
You shall not add to the word which I command, neither shall you diminish anything from it, that you may keep the commandments of the LORD your God, which I command you.
Yet, amazingly, in the doctrine of Divrei HaSoferim, we can see the rabbinical ruling that rabbinical, oral traditions are to take precedence over written scriptures:
Pesachim 115a: …in the case of a scriptural and rabbinical precept, the rabbinical one comes and nullifies the scriptural one.
Pesikta Rabbati Section 3 – A person must not say, “I will not keep the commandment of the elders (Rabbis) because they are not from the Torah.” The Almighty says to such a person, “No, My son! Rather, all that they decree upon you, observe! As it is written, according to the instruction which they teach you (Deut. 17:11). Even I (YHWH) must obey their decree, as it is written, you will decree and he will fulfill” (Job 22:28).
In the last sentence, the Pesikta Rabbati has the audacity to state that even God must obey the decree of the Rabbis. This is a blatant example of erroneous human reasoning. Do not follow your teachers blindly, lest you fall into a pit.
The written scriptures may not make complete sense to us, and we may not be able or know how to follow them all – but in regards to rabbinic traditions and oral law, it may be safest to follow the teachings of our great high priest, Jesus of Nazareth, who was not silent on the matter.