What does the Bible say about the blindness of the Pharisees?

In the context of John 9, the Pharisees represent those who, despite their religious knowledge and authority, failed to see the truth of who Jesus was. Jesus called them out in John 8:42, stating that their father was the devil. Their spiritual blindness was a result of pride and an unwillingness to accept the truth revealed in Christ, which serves as a warning to all believers to be cautious of false teachings that can lead them away from the truth of the gospel. Therefore, the emphasis here is on the necessity of divine revelation for true understanding.