Yeasts are microorganisms classified in the Fungi kingdom. Yeast permeates the dough and
converts the sugars into carbon dioxide. This gas causes the dough to rise when pockets or
bubbles of gas are formed. The presence of yeast affects the whole batch of dough. The yeast determines what the bread will look like. Even though yeast is small and produces invisible
gas its presence will leave a visible impression on the bread.
Jesus and the disciples were crossing the Sea of Galilee to dock at Bethsaida on their way to Caesarea Philippi. Apparently, the disciples had forgotten to bring bread for the trip but had not
yet told Jesus. In the boat on their way to Bethsaida Jesus says, “Beware of the yeast of the Pharisees and Sadducees.” Because the disciples are so concerned with having forgotten to
bring bread and, most likely, are blaming each other for the oversight (Think children traveling
in the back seats of the family van!) they miss Jesus’ point completely thinking he has
discovered (or, divinely knows) of their blunder.
Instead Jesus was warning against the teaching of the groups that opposed his claim to being
the Messiah. Jesus was not warning against the scriptures that the Pharisees and Sadducees
used, but against their teaching and commentary concerning those scriptures.
Poor teaching, inaccurate interpretation, or selectively twisting verses out of context is dangerous
and is much more destructive than many recognize. Bad doctrine is just like the microorganism called yeast, which is virtually invisible and produces a gas that is unperceivable. The effect of
yeast altars the final shape, texture and taste of the bread. So does Bible teaching, doctrine and theology altar the thoughts, words and actions of a believer. Some Christians may be completely unaware of its presence, but teaching (or, lack thereof) does leave a visible impression on the life
of a believer.