the yeast of the pharisees and sadducees

"be on your guard aginst the yeast of the pharisees and sadducees" (matthew 15:6)

after witnessing the miraculous feeding of five thousand people with a few fish and a few loaves of bread, and then the feeding of four thousand people with similar meagre resources, the disciples were still worried that they wouldn't have something to eat that day, having "forgot[ten] to take bread" when they went across the lake. Jesus rebukes them for having such "little faith". didn't they know by now that if Jesus were in the midst of them that they would never go hungry? apparently they needed reminding, even after witnessing with their own eyes these wondrous miracles. Jesus reminds them visually of the picture of so many basketfuls of food left over after everyone was fed. we mustn't be too hard on these poor disciples. are we not exactly the same? we praise God for the provision of something we have prayed for, but then immediately worry and complain about the next need that we perceive is not being met.

Jesus is far more concerned that we expend our energy, not on worrying about what we will eat, but on being on our guard against the "yeast of the pharisees and sadducees". He is telling us that even the tiniest, most minuscule seed of hypocrisy, legalism, self-righteousness, laziness, pride, arrogance, hatred, judgmentalism, hard-heartedness, cynicism, and unbelief, will slowly infiltrate our mind and our hearts deep from within, and eventually corrupt the whole inner spirit. He is imploring us to guard our hearts against every evil.

what an important command Jesus gives us! how can we undo or "reverse" the corrupt images we have seen, the gossip we have heard, words and thoughts that dishonor God and each other? about as easily as undoing or reversing the spreading of yeast through a loaf of bread.