The problem was Jews in first century Israel followed their own doctrines instead of the written word of God.
In first century Israel, The sect of Pharisees (the Pharisees, the scribes, and all Jews who belonged to the sect of Pharisees) obeyed Traditions of the Elders.
Jesus Christ criticized the Pharisees and the scribes for obeying Traditions of the Elders which nullified the word of God (Matthew 15, Mark 7). That's why the biggest opponents of Jesus Christ were the Pharisees and the scribes (Matthew 23, Luke 11).
Apostle Paul called Traditions of the Elders as "Traditions of our fathers" in Galatians 1:14 and Jewish Priest Josephus calls "Traditions of the Elders" as "Tradition of our forefathers."
"What I would now explain is this, that the Pharisees have delivered to the people a great many observances by succession from their fathers, which are not written in the laws of Moses; and for that reason it is that the Sadducees reject them, and say that we are to esteem those observances to be obligatory which are in the written word, but are not to observe what are derived from the tradition of our forefathers." (Antiquities of Jews Book XIII.X.VI).
Traditions of the Elders later came to be known as Talmud. This is also agreed by Jewish society.
Rabbi Michael Rodkinson - "The Talmud, then, is the written form of that which, in the time of Jesus, was called the Traditions of the Elders, and to which he makes frequent allusions" (Source - The History of the Talmud, Vol. II, page 70, Chapter IX).
As mentioned above by Josephus, the sect of Sadducees opposed Traditions of the Elders.
Although the Sadducees encouraged to follow the Old Testament, still the problem with the sect of Sadducees was that they followed their own doctrine.
The Sadducees say that there is no resurrection, neither angel, nor spirit while Pharisees acknowledge all these things (Acts 23:8).
Josephus (Jewish Wars 2.8.14) on the Sadducees - "But the Sadducees are those that compose the second order, and take away fate entirely, and suppose that God is not concerned in our doing or not doing what is evil; and they say, that to act what is good, or what is evil, is at men's own choice, and that the one or the other belongs so to every one, that they may act as they please. They also take away the belief of the immortal duration of the soul, and the punishments and rewards in Hades. Moreover, the Pharisees are friendly to one another, and are for the exercise of concord, and regard for the public; but the behavior of the Sadducees one towards another is in some degree wild, and their conversation with those that are of their own party is as barbarous as if they were strangers to them. And this is what I had to say concerning the philosophic sects among the Jews."
In Matthew 22:29, we see Jesus Christ telling the Sadducees about their lack of knowledge in the scriptures and in the power of God.
Jesus Christ points out that Jews didn't believe in him, because they never believed the laws of Moses and they also didn't keep the law of Moses. In Acts 7, Stephen also points out that Jews didn't obey the law and they persecuted and killed the prophets of God.
John 5:46-47 (NIV) - "If you believed Moses, you would believe me, for he wrote about me. But since you do not believe what he wrote, how are you going to believe what I say?”
John 7:19 (NIV) - "Has not Moses given you the law? Yet not one of you keeps the law. Why are you trying to kill me?”
Acts 7:52-53 (NIV) - "Was there ever a prophet your ancestors did not persecute? They even killed those who predicted the coming of the Righteous One. And now you have betrayed and murdered him— you who have received the law that was given through angels but have not obeyed it.”
Jesus Christ and the followers of Jesus Christ opposed these Jews due to the fact that they followed their own doctrines instead of the written word of God.
That's why Jews persecuted early Christians. Apostle Paul wrote about the attitude of these Jews.
1 Thessalonians 2:14-16 (NIV) - "For you, brothers and sisters, became imitators of God’s churches in Judea, which are in Christ Jesus: You suffered from your own people the same things those churches suffered from the Jews who killed the Lord Jesus and the prophets and also drove us out. They displease God and are hostile to everyone in their effort to keep us from speaking to the Gentiles so that they may be saved. In this way they always heap up their sins to the limit. The wrath of God has come upon them at last."
The generation of first century Israel was extremely evil, because they followed their doctrines instead of believing God, his son Jesus Christ, the Holy Spirit, and in the written word of God.
On several occasions, Jesus Christ calls his generation in first century Israel as "wicked/sinful and adulterous generation" (Matthew 12:39, Matthew 16:4, Mark 8:38, etc.).
Jewish Priest Josephus agrees with Jesus Christ on the wickedness of that generation.
"I shall therefore speak my mind here at once briefly: — that neither did any other city suffer such miseries, nor did any age ever breed a generation more fruitful in wickedness than this was, from the beginning of the world." (Josephus' Jewish Wars V, 10:5).