Should we obey the Pharisees who converted to Christianity after Jesus died? NO. Jesus warned his followers about the leaven of the Pharisees.
It started almost immediately after Jesus died. Even though Pharisees like the Apostle Paul were very sincere Christians, they also introduced the 'leaven' of the Pharisees into the early Christian congregation.
The Pharisees were more educated and self righteous than the people Jesus associated with. Their power, influence, social status, and importance led them to teach doctrines that conflicted with the love Jesus taught. Their self-righteous attitude and judgment of those not as worthy, was the 'leaven of the Pharisees'.
Even though the Pharisees rejected Jesus and plotted to kill him, they were not 'evil'. They were strong supporters of religious tradition and the rules of Jehovah. Jesus was a threat to their way of life. The Pharisees thought that Jehovah was on their side because they were teachers of God's law. After Jesus died, and some of the Pharisees like the Apostle Paul converted to Christianity, it was natural for them to introduce some of their beliefs into the early Christian congregation. It would be like a JW Elder becoming a Catholic and then becoming the Pope. Could a zealous JW suddenly abandon every single one of their beliefs about holidays, blood transfusions, political neutrality, etc? Of course not. The Pharisees who became Christians took their beliefs with them when they converted to Christianity. Due to the influence of the Apostle Paul and other Pharisees, the message of Jesus changed after he died.
The Pharisees didn't see any harm in adding a few rules and doctrines into the early Christian congregation. After all they were very educated and highly qualified to explain the laws of Jehovah. The only problem was that Jesus is the path to eternal life. All authority was given unto him, - not the Pharisees. Matthew 28:18; Jesus warned us about the leaven of Pharisees and why we should ignore what they have to say. Luke 12:1; Matthew 16:6; Matthew 12:11
The Apostle Paul was a Christian, but he also claimed to be a Pharisee at the same time. The Bible shows that other Pharisees joined the early Christian congregation and added their wisdom to the message of Jesus. Acts 23:6; Acts 15; Get The Facts About The Apostle Paul
The Pharisees taught us to judge the wicked. They taught us about Jehovah's rules and how to be separate from non-believers who are not as righteous as us. 2 Cor. 6:14,17; The Pharisees rejected Jesus when he was alive and took their beliefs with them when they became Christians. Mark 3:1-6; Luke 22:1,2
Did Jesus teach us to judge and be separate from those not as righteous as us? No he did not. Luke 6:35. This was the work of the Pharisees who became Christians after Jesus died.
Christian Pharisees like the Apostle Paul paid a dear price and suffered greatly according Paul's personal account. 2 Cor.6:3-13; However their attitude of superiority, judgment and self-righteous was the leaven of the Pharisees. 2 Cor. 6:14-18.
No matter how sincere, the Pharisees did not have the mind of God. Jesus is the path to eternal life. Not the Pharisees. Luke 6:27-41; John 3:36