Learning more about the Pharisees
As we have seen in Chapter 23 of Matthew's Gospel, Jesus frequently attacked the Pharisees for their hypocrisy. Their name perhaps comes from a Hebrew word meaning "separated ones". They argued that the oral tradition of the Law (wich they believed had been handed to Moses by God) was as important as the written tradition. Through this concern came the Talmud (the written record of the oral tradition which was completed in the 4th century AD) and the Masoretic Text (which was the original Hebrew Bible). Their work led to the careful preservation of the Old Testament, and their concern to spread the oral tradition to the ordinary people was laudable.
The New Testament mostly shows the Pharisees as a religious sect (like others - the Sadducees or the Essenes), and at times suggests they have quite a bit of political influence. However they are most commonly seen as a religious sect within Judaism. While the Pharisees affected Judaism in many positive ways, in the New Testament, their reliance on the oral tradition is often portrayed as overly legalistic, and in some cases a means of getting around the Law.
The Pharisees saw Jesus as a threat to their kind of interpretation of the Law of Moses, and they continually try to trap him into making a blasphemous statement or into saying something that Rome will find a threat so that he can be denounced.