"A little leaven the whole lump is leavening."
-A little leaven leavens the whole lump. A lot of people have heard this phrase, no doubt. But what does it mean, exactly? Well, leaven is yeast, and you only need to add a little bit of yeast to get the whole loaf of bread to rise. The thing about leaven is that it does make a more desirable loaf of bread, and it does only take a little, but it also takes special conditions and some extra time in order for the dough to rise once the leaven has been added. The relevance is perhaps somewhat lost on modern Gentiledom, and honestly was probably lost at least to a certain extent on this mostly Gentile assembly, but leaven was a significant part of Jewish culture, since unleavened bread played an important role in their religious observances. It refers back to the time of the Exodus, when the nation Israel had to leave Egypt in haste and did not have time even for their daily bread to rise, and so they made unleavened bread. This then was later memorialized in the feast of Passover, where the Lord instructed them to eat unleavened bread for an entire week as they remembered how He had delivered them from their slavery in Egypt. During that week in fact they were to clean out all leaven from their homes and not to let any even be found anywhere in their territory.
-Onto this foundation of the historical significance of leaven, Jesus Himself added another layer when He described the (false) teaching and hypocrisy of the Pharisees as leaven. In this He was capturing the idea that it only takes a little bit of false teaching, just a little bad information, a little hypocrisy, to spoil the entire batch. And truth be told, given a choice between unleavened bread and leavened, most people will indeed choose the latter (those yeast rolls you get at places like Golden Corral and Texas Roadhouse are hard to resist!). It may make a message or teaching sound more appealing, more desirable, easier to swallow and digest, but the reality is that no amount of bad information is a good thing. Not ever. Even a little bit can (and will) ruin the whole thing. The teaching of these Judaizers was leavened, what with their emphasis on works and circumcision and on keeping the Law. That bit of bad info ruined the entire batch. So may your dinner rolls be full of yeast and yummy goodness, but for your intake of Bible teaching, go unleavened. When it comes to teaching which impacts our pursuit of Jesus, that which has eternal implications, we need to be doubly diligent to clean out every last tiny bit of leaveny bad information and not let any be found anywhere near our home or our assembly. Our (eternal) life - and that of our family and friends - very likely depends on it.