If you walk into my kitchen, it might appear at times like a laboratory. Meg and I brew our own kombucha, several gallons of which sit on the countertop, happily fermenting away. We also make our own yogurt, kefir, and lactofermented vegetables, carrots mostly. We’re next thinking about making our own sourdough.
It’s as easy as it is fun. All you do is ready the raw ingredients and let nature do the rest.
Each of these preparations involves living, active cultures that transform the ingredients from one thing to another. Back it up a step and kombucha is just sweet tea, yogurt is just milk, etc. But the added cultures — just a small amount — metabolize the sugars they find in the ingredients, grow, and permanently alter the product. What started out as one thing becomes another, and it happens while you’re not looking.
Jesus actually taught about this, and his words can both inspire and warn us about little things changing our lives in big ways.
Leavening the lump
We’re perhaps familiar with the Mosaic ban on leaven around Passover. These days there are several different kinds of leavening, but the Bible is talking about the living kind, like yeast or sourdough starter, that runs rampant through a lump of dough.
This is the image Jesus conjures in the parable of the leaven, in which he describes the kingdom of heaven as a woman adding a little leaven to her dough to see it spread throughout the entire lump. Because of the fermentation process, the leaven transforms the dough in which it is placed.
Commenting on this passage, Irenaeus identified Jesus himself as the leavening agent. The idea is that once Jesus gets into you, he can take over your whole being. Once the kingdom starts growing, it can’t be stopped.
But there’s another kind of leaven mentioned in the gospels as well: the leaven of the Pharisees. Jesus tells the disciples to beware this leaven, which he soon explains as the Pharisees’ teachings. The warning is clear enough. Once their ideas infect you, they can corrupt your whole person.
Whether it’s wine or beer, kombucha or yogurt, you have to be careful that errant bacteria do not get into your product. Without good sanitation, something may sneak in and ruin your work, throwing off funky flavors and even spoiling the whole batch.
And that’s true for the Christian life is well. Certain doctrines and dispositions can be very disruptive to our spiritual growth. Just think about how certain doctrines might engender pride or acquisitiveness. What about envy and discontent? And they can spread and spoil without our awareness. If you smell the funk, the damage is already done. That’s exactly why we have to be on guard, as Jesus directed.
It’s interesting to me that there’s a linguistic connection between fermenting cultures and our beliefs. Both are connected by the word cultus, which implies both work and worship, labor and liturgy.
Jesus’s analogy to leaven makes the connection. The kingdom spreads and grows and so does corrupting doctrine. We benefit from actively cultivating the former while guarding against the latter.
Paul indirectly picks up the same connection, and it’s from his letters to the Galatians and Corinthians that we get the phrase, “A little leaven leavens the whole lump.” That’s what leaven does. Let’s make sure we’ve got the right kind.