"Then He left [the Pharisees and Saducees] and went away. When the disciples crossed the sea, they forgot to take any bread. And Jesus said to them, 'Look out, and keep on guarding yourselves against the yeast of the Pharisees and the Sadducees!' Then they began to discuss it among themselves, and said, 'It is because we did not take any bread.' Jesus knew it and said, 'Why are you discussing among yourselves the fact that you have no bread? Have you so little faith? Do you not understand yet? Do you not remember the five loaves for the five thousand and how many basketfuls you took up? Nor the seven loaves for the four thousand and how many hamper-basketfuls you took up? How is it that you do not understand that I did not speak to you about bread, when I said, keep on guarding yourselves against the yeast of the Pharisees and the Sadducees?' Then they understood that He meant, guard yourselves not against yeast for bread, but against the teaching of the Pharisees and the Sadducees."Commenting on Matthew 16.6, Clarke writes:(Mat 16.4b-12 WmsNT)
Beware of the leaven - What the leaven of Pharisees and Sadducees was has been already explained, see Mat 16:1. Bad doctrines act in the soul as leaven does in meal; they assimulate the whole Spirit to their own nature. A man’s particular creed has a greater influence on his tempers and conduct than most are aware of. Pride, hypocrisy, and worldly-mindedness, which constituted the leaven of the Pharisees and Sadducees, ruin the major part of the world."The destruction of the world through three things: pride, hypocrisy and worldly-mindedness. Yes, that will pretty much do it.