What was wrong with the Pharisees that they deserved such a harsh rebuke from Jesus in the Gospel reading today?

The Pharisees were expositors of the law. They were a sect within Judaism dedicated to the observance of the law. This meant that their whole life was dedicated to interpreting the law. What was missing from them then? The answer is that in spite of the fact that their whole life was dedicated to the law, there was no 'heart' in what they did. Legalism ruled them rather than a genuine inner desire to do what pleased God. They put the obligation of the law onto people in the most severe manner. They were people who claimed to live by the law but missed the whole point of the law. The law was supposed to help people to live a life that was in harmony with God but this was no longer the case with the Pharisees of Jesus' time.

Jesus spoke rightly when He said that they imposed heavy burdens on the people. The Pharisees insisted on meticulous observance of the 613 commandments (365 probibitions and 248 prescriptions) and in the end all of this became more important than God Himself.

For us today, it is good to check and see whether we have the most basic thing in our Christian life, that is, a one to one relationship with God.