Now they had forgotten to bring bread, and they had only one loaf with them in the boat. And he cautioned them, saying, “Watch out; beware of the leaven of the Pharisees and the leaven of Herod.” And they began discussing with one another the fact that they had no bread. And Jesus, aware of this, said to them, “Why are you discussing the fact that you have no bread? Do you not yet perceive or understand? Are your hearts hardened? Having eyes do you not see, and having ears do you not hear? And do you not remember? When I broke the five loaves for the five thousand, how many baskets full of broken pieces did you take up?” They said to him, “Twelve.” “And the seven for the four thousand, how many baskets full of broken pieces did you take up?” And they said to him, “Seven.” And he said to them, “Do you not yet understand?”
A mere pinch of yeast used in bread-making will influence and make the whole lump of dough swell up. Yeshu was saying that the concerns of the Pharisees and Herodians, for example with worldly and political matters, preoccupied them so totally that it was like the influence of yeast.
Yeshu said, “Don’t be taken up with concerns like theirs. Where is your believing spirit? Why are you being so preoccupied with bread when taking part with me in my work? or if you go where I send you?” (See Mark Chapter 6 verses 7 to 13)