Leaven or yeast is an active agent that causes change and corruption of the original ingredients. That is why yeast often symbolizes sin in the Scriptures. A little of its influence goes a long way.
Yeast is the same ingredient that causes fermentation in alcoholic beverages. The expansion pressure causes the wine cork to pop when opened.
This is not a rant against what you eat or drink, but about what influences your spirit. When we do not deal with sin in ourselves or in the church, there is a corruption causing change to the original substance.
How has sin changed the purity of your faith? Jesus warned his followers about corrupting influences.
At first read we are struck with the inability of the disciples to understand what Jesus is talking about. They are being warned about bad influences and instead they think Jesus might be talking about their lack of bread.
They are doing what we often do when we hear warnings. We interpret and do what we think is best. The speed limit is posted at 100 kph, but we have heard that the police will not bother you unless you are more than 15 kph over the limit. So we set our cruise control to 117 kph. We see the warning and we think it does not apply fully to us. We even resent those who obey the speed limit, since they slow us down.
Don’t accept the limit—set your own. Our attitude toward authority is suspect.
The discussion began because the disciples had a bread shortage. Someone was responsible for the oversight and thoughts of hunger were creeping in. When Jesus warns about the leaven of the Pharisees and the leaven of Herod, they focus on what is bothering them, not on what concerns Jesus.
It is often in our nature to defend and minimize our responsibility when we are warned or corrected on some matter. This is our sin sickness that Jesus persistently speaks to. What has influenced us so that we are incapable of understanding the words of loving correction? Why do we feel the need to be defensive and explain ourselves away?
The disciples did not see what Jesus saw. The lack of bread was a cause for them to assign blame, be worried about their comfort and be dull in hearing Jesus’ concern. Jesus saw dangerous mindsets that affected their daily life. There were two influences in particular that they needed to be aware of.