The Pharisees were strict, but wrong in their interpretation of the Scriptures. They were wrong primarily because their strictness was in the area of ritual purity and morality than true spirituality and ethics. Both by Jesus' and Paul's testimony, they were not living according to God's commandments as a way of life. Paul states clearly: "For not even those who are circumcised keep the law, but they desire to have you circumcised that they may boast in your flesh" (Galatians 6:13).
A number of years earlier, Jesus said virtually the same thing, recorded in a couple of places:
"And in vain they worship Me, teaching as doctrines the commandments of men." For laying aside the commandment of God, you hold the tradition of men - the washing of pitchers and cups, and many other such things you do. (Mark 7:7-8)
Mark 7:1 verifies that He was speaking to the Pharisees. They were zealously and religiously adhering to Halakah, which was an interpretation of both the written law, given at Mt. Sinai, and a collection of verbal or oral laws that had been passed from one generation to the next for centuries. This law they elevated to divine status. In so doing, they rejected the commandments of God.
When some in the Jewish faith merged their zealous practice of Halakah with Gnostic concepts, they became a persuasive and persistent enemy of the church. Gnosticism played a significant, background role in what Paul wrote in the book of Galatians.