Today Jesus warns His disciples against the 'yeast' of the Pharisees. Yeast causes fermentation and, in the making of bread, makes the dough rise. The Jews saw this fermentation as a kind of corruption and that is the meaning of Jesus' words here. The corruption of the Pharisees was their hypocrisy - so observant and law-abiding on the outside but full of hate and judgmentalism on the inside. Jesus' disciples, on the contrary, have to be fully open and the teaching they have received in private will one day be broadcast from the housetops. That will be the time when they will be in danger. The Gospel's message of love and justice is seen as threatening by so many. So they will be criticised and some of them will even be in danger of being killed for their Gospel beliefs. But they are not to fear. God is aware of everything and is with them. We, too, are called to live our faith openly and need to be ready for negative reactions. As Jesus said, the disciple is not better than the Master.