The Pharisees {\cf2\super [214]} and Sadducees {\cf2\super [215]} came to Jesus. They wanted to test Jesus. So they asked Jesus to show them a miracle {\cf2\super [216]} to prove that he was from God.
Then the followers understood what Jesus meant. Jesus was not telling them to guard against the yeast used in bread. Jesus was telling them to guard against the teaching of the Pharisees and the Sadducees.
Jesus said to the followers, “Be careful! Guard against the yeast {\cf2\super [219]} of the Pharisees {\cf2\super [220]} and the Sadducees. {\cf2\super [221]} ”