Why is the leaven of the Pharisees condemned in the Bible?

In the context of Mark 8, the leaven of the Pharisees represents the self-righteous attitude and hypocrisy of the religious leaders who falsely believed they could earn God's favor through their own efforts. Jesus warns His disciples to beware of this leaven, indicating that even a small amount can corrupt one’s entire understanding of righteousness. By referencing the twelve baskets left over from the feeding of the five thousand, Jesus illustrates that no matter how much effort we put into following the law, it is never enough; only by grace can we be truly saved. This condemnation serves as a reminder for believers to rely solely on Christ's merits, not their own, for salvation.