After feeding the four thousand with seven loaves and a few small fishes, Jesus, having crossed the lake, was met on the other side by certain Pharisees, whose attitude towards him was such that he betook himself again to the boat. On the way back across, the disciples realized that they had but a single loaf. Jesus, still thinking of the Pharisees, and desirous of destroying their influence on his disciples, began to warn them against them. In so doing he made use of a figure they had heard him use before—that of leaven as representing a hidden but potent and pervading energy: the kingdom of heaven, he had told them, was like leaven hid in meal, gradually leavening the whole of it. He now tells them to beware of the leaven of the Pharisees. The disciples, occupied with their lack of provision, the moment they heard the word leaven, thought of bread, and imagined perhaps a warning against some danger of defilement from Pharisaical cookery. The leaven like that of the Pharisees was even then at work in their hearts; for the sign the Pharisees sought, they had had a few hours before, and had already, in respect of all that made it of value, forgotten.
It is to the man who is obedient to the word of the Master, that the word of the Master unfolds itself. For life, that is, action, is alone the human condition into which the light of the Living can penetrate; life alone can assimilate life, can change food into growth. See how the disciples here fooled themselves!