Here's a todays history lesson.
The Sanhedrin was the ruling party in Jesus day and their appointment started with Moses. You could say they were the Supreme Court when it came to matters of the law, which are of course the Scriptures.
Prior to the birth of Jesus, Rome occupied Israel and appointed Harod as king. Harod was a vile man who killed his own sons because he thought they were threats to his throne. He also killed many children hoping to kill Jesus, but he didn't succeed.
When Harod was appointed King of Israel, his first task was to secure the law of the land, which is to say he needed to control the Supreme Court aka the Sanhedrin.
As a result, whoever would now succumb to his rule, which is to say whoever would not deny scripture to support him was put to death and a new yes man was appointed.
Many times Jesus explains the law to the Sanhedrin. In part, this is because they honestly did not know the basics of the law. Jesus wasn't the only one who had to explain the law and another fellow named Hillel helped teach them and became a Sanhedrin himself.
We see Jesus at the temple when he was 12 and at that time, Hillel was leading council. Ironically, there are no disputes and they are amazed at his knowledge.
Forward another 15 years and Hillel was replaced by a teacher named Shamia as ruling council within the Sanhedrin courts and it was within this context Jesus has much to say and they are no longer amazed at his teachings.
Jesus had become a national threat to King Harod (not to be mistaken for his Father who was King first) and its alliance to Rome. Members of the Sanhedrin such as Nicodemus were already turning toward God and if this movement continued, the Supreem court would no longer be subject to the Kings rule under Rome, but rather it would go back to biblical rule.
In part, this is why the ruling party of the Sanhedrin wanted Jesus dead.