The Pharisees knew the Old Testament, but did not understand what it meant. They did not grasp that God's law, and the history of Israel, were written to prepare people to submit to Jesus as the King who is greater than David. Those religious leaders thought God would be pleased with obsessive rule-keeping, so they made up more and more difficult rules for the people to obey. All that diverted attention from God who was not demanding holiness by discipline, but wanted to give Himself for them. So the very people who were supposed to draw people closer to God were actually pushing them away: instead of directing them to heaven they were cultivating them for hell (Matthew 23:15).
 
Truth is like a plant. It starts as a seed and grows into a plant which will reproduce itself. Jesus said that false teachers are weeds that multiply their error and are useless to the farm owner. They corrupt the people who listen to them like the seeds of weeds infect the soil around them. But, Jesus said, leave them alone. It was not the job of the apostles to use up their time and energy in fighting the religious establishment. The good gospel seed will do its own work of bringing up godly disciples, and showing up those who were not.
 
Of course, some Pharisees did trust in Jesus: Nicodemus, Joseph of Arimathea and Saul who was renamed Paul. Paul taught about Jesus - comparing the Old Testament prophecies with accounts of His life, death and resurrection. When religious leaders questioned him, Paul gave Biblical answers, but when they became hostile, he moved on or trusted the Lord in persecution. The apostles did not fight their critics: they just spoke about Jesus and lived to please Him. Those who believed were saved, and those who refused to believe would continue having no place in Christ's kingdom.
 
False teachers certainly do a lot of damage. Watching on, we can see how they are infecting other people and our natural instinct is to stop them. But Jesus looks long-term. He sees the people who want to be seduced as well as those who seduce them away from the truth. Both will fall into the pit of hell. Instead of fighting, the apostles declare Jesus Christ as the Saviour of the world. We are called to share, teach, preach, exhort, rebuke, correct, teach and train ... but not to fight the false teachers (Luke 9:51-55). They have no place in the ministry and will be pulled up in God's time. We need to forsake fleshly battles with the obstinate and keep on sowing the good seed, among our family, friends and colleagues. Don't worry about those who oppose you, seek out the seekers - there are many of them!