Read: Matthew 16; Mark 8
Marked: Matthew 16:6, Then Jesus said to them, “Take heed and beware of the leaven of the Pharisees and the Sadducees.”
The Pharisees and Sadducees were the religious leaders and teachers in Israel, but often could not agree on the most basic of Scripture. Both parties added to and took away from Scripture to meet their own objectives and Jesus took them to task for this.
This was their sin and leaven is used here as a euphemism for sin and I must be careful not to allow the leaven of the Pharisees and Sadducees to affect my observation of Scripture.
It is, after all, the Word of God and I cannot alter or change His Word but must be faithful to it. To do otherwise would be sin.