They had converted the devotional teachings of Abraham, Moses, Joshua, Eli, Samuel, David, Solomon and all the other prophets into empty ceremonies and rituals, supported by an ecclesiastical hierarchy with appointed teachers. Meanwhile, as Jesus is clarifying, they did not even practice what they preached.
Those original instructions by God through His messengers (the "prophets") were meant to help those of previous generations come closer to Him. The high priests and pharisees were utilizing those teachings to maintain their authority and positions of power. Meanwhile, they did not have the vision to recognize God's representative, Jesus.
Because they maintained legal authority over the people, Jesus is recommending they follow the rules and regulations maintained by these leaders. If Jesus had advised them not to follow the rules, this could subject them to harsh punishment, and Jesus did not want that. He recognized these Jewish leaders were connected to the Roman government. While the Romans had ownership over the lands, the Jewish leaders coordinated the governing of the people with the Roman governors.
Jesus, on the other hand, wanted to change people’s hearts and re-introduce them to God. He did not want to interfere with the system governing of the people.
There is an important lesson within Jesus' statement - and the situation that had developed among the Jews. The tendency to convert the instructions of a previous teacher - intended to help those of that culture and society re-establish their relationship with the Supreme Being - into empty rules and rituals with ecclesiastical authority has occurred repeatedly in history. This has occurred not only among Jewish sects, but also among many of the sectarian institutions around the world.
What is it that drives humans to take the teachings of a previous teacher, and turn them into an organizational power structure? If we look around at all the organized sectarian institutions of today - most of which maintain that their religion is the right one and all the others are the wrong ones - we find a consistent pattern: We find ecclesiastically appointed leaders who maintain empty rituals and ceremonies supposedly supporting a particular historical teacher, while leaving behind the essence of their teachings.
What causes this? Our quest for power. Our quest for authority. Those of us living within the physical dimension in these physical bodies are here because we rejected God. Why? Because we do not want to worship and serve God: We want to be worshiped and served (see Garden of Eden for further discussion).
For this reason, we humans will utilize whatever means available to us to gain authority and power over others. It doesn't matter whether the means happens to be the teachings of God's representative. We will manipulate those teachings in order to create organizational structures that exert authority over others.
This is precisely what the Roman emperor Constantine did with the teachings of Jesus. He realized the influence of Jesus' teachings could be used to his own political advantage. He could control the people by creating an institution that exerted authority over people. So Constantine collected together teachers from different regions (the Synod of Nicea) and coerced them to formulate a single doctrine regarding Jesus (the Nicene Creed), which every church had to (by law) synchronize with. Then he ordered a politically-motivated selection of certain scriptural texts and appointed scribes to combine and translate those texts into a cohesive single book, the Bible. (Other scripture texts were ordered to be burned.) This became the official scripture of the official Church sanctioned by the Roman empire - the early Roman Catholic Church.
Like the situation Jesus is discussing regarding this Jewish institution, this new ecclesiastical organization set up by the Roman emperor became law. Eventually, people were required to attend Roman Catholic mass. If they didn't, they would be condemned, and hung or burned at the stake. It didn't matter that the priests of this ecclesiastical church did not actually teach what Jesus taught. And it didn't matter that the Bible was translated to Latin - a language not understood by most Europeans. And it didn't matter that masses were ritualistic ceremonies spoken in Latin either. So the people were forced to sit in mass and listen to empty Latin phrases while making the ritualistic motions. Many of these rituals still take place today among Catholic churches.
This coerced power structure replete with empty rituals called the Roman Catholic Church virtually controlled the Christian world for over a thousand years. During this period so many atrocities were committed by this institution. Many innocent people were slaughtered. Many people were tortured - in the name of Jesus. This is why Jesus also said:
“Not everyone who says to me, 'Lord, Lord,' will enter the kingdom of heaven, but only he who does the will of my Father who is in heaven. Many will come to me on that day, ‘Lord, Lord, did we not prophesy in your name, and in your name drive out demons and perform many miracles? Then I will tell them plainly, ‘I never knew you. Away from me, you evildoers!” (Matt. 7:21-23)It wasn't until a few fearless English and German persons decided that enough was enough in the fourteenth and fifteenth centuries - such as John Wycliffe, Jan Hus and Martin Luther - that some change came. Even then, those who translated the Bible into English and other common languages were sought out and persecuted by the Roman Catholic Church.
In other words, the very same situation (but on steroids) that Jesus was criticizing in this statement about the Jewish pharisees and priests took place in Jesus' name after he left the planet.
And even today, we find so many ecclesiastical Christian and Jewish sects that are led by appointed teachers who teach empty rules and rituals, while they themselves utilize their positions of authority, some to even abuse their parishioners, instead of abiding by their own rules. They feel above their own laws. This is the result of the desire for authority and power.
Jesus taught the opposite of this. He taught humility, compassion and caring for others. And above all, he taught that our focus should be upon loving and serving God, not on gaining positions of authority:
“‘Love the Lord your God with all your heart and with all your soul and with all your mind.' This is the first and greatest commandment.” And the second is like it: ‘Love your neighbor as yourself.’ All the Law and the Prophets hang on these two commandments.” (Matt. 22:37-40)
(For a translation of Jesus' statements from the Book of Matthew without institutional sectarian influence, see the Gospels of Jesus - translated from the original Greek texts.)