you then who teach others, do you not teach yourself? While you preach against stealing, do you steal? (ESV)
Have you ever known someone who seems to be always pointing out everyone else's faults? Do you find yourself wanting to hang around them all the time? Or would you rather avoid them like the plague. I am going to assume you would rather not be around them. The Apostle Paul used to be one of those people. That was when he was a Pharisee. Then Christ changed him.
The Pharisees were the teachers of the Law. It might have been one thing if they simply taught the Law. There was certainly a need for the people of Israel to know God's Law. The problem with the Pharisees was that they not only taught the Law, they added to it! They added so many burdensome laws that it was even more impossible to keep them. In fact, the Pharisees did not keep the Law.
Paul says to those who are so adamant about teaching others all of the profound wisdom they have obtained from the law, "Do you teach yourself?" He is asking if those who are obsessed with the Law are not actually law breakers themselves. I imagine that you do not like being around a judgmental phony. God is not a fan either. Listen to what Jesus said about the Pharisees.
Then Jesus said to the crowds and to his disciples, “The scribes and the Pharisees sit on Moses' seat, so do and observe whatever they tell you, but not the works they do. For they preach, but do not practice.
There is a danger for those who teach. You must match your words with your actions. A proper approach to knowledge is humility. Those who are proud simply hurt others by their phony judgmental attitude.