"Watch and beware of the leaven of the Pharisees and Sadducees."
When Jesus said this to the disciples, they could not make sense of it because they were worried about having forgotten provisions for their journey. They had just witnessed, prior to setting out, a confrontation between those Pharisees and Sadducees and our Lord. But is clear they did not understand what He had said either.
"And the Pharisees and Sadducees came, and to test him they asked him to show them a sign from heaven." Clearly feeding four thousand people was not "sign" enough for them. Nor were any of the other miracles Jesus had performed. The truth is that they wanted no sign of Christ's authenticity. Anything Jesus did was, for them, merely proof of what they had already chosen and determined to believe about Him. After all, they even refused the sign of Jonah that later was right in front of them.
Which brings us to Jesus and his disciples "on the other side." The disciples had already seen Jesus feed multitudes. Twice. These actions should have told them, "I will nourish you." They had seen him walk on water and quell a storm." This should have told them, "I will protect you."
Only after Jesus had explained, had put into context where He stood on the matter of bread, did they get it: "he did not tell them to be aware of the leaven of the bread, but of the teachings of the Pharisees and Sadducees." For these who had chosen to be enemies were looking to destroy, and their teaching could not do otherwise.
Lord, make us open to your teaching and aware of those whose interests blind them. Help us to read the true signs of Your life and words and thus share in Your joy and creation. Amen.