The parable of the leaven is similar to the parable of the mustard seed in that both speak of the kingdom of heaven as something that starts out with small, seemingly insignificant beginnings and slowly develops into something enormous. Much of what I said in the previous post about the nature of God's kingdom would apply here also.
My initial thought with this parable was to compare yeast granules to the mustard seed and talk about how potent they both are. But now it occurs to me that the woman in the parable probably did not view yeast as something you buy from a grocery store in those little Fleischmann's paper packets that come in sets of three. When I cut those packets open with a scissors and sprinkle out the yeast, I see tiny brown granules, separate, dry, and inactive until I add warm liquid. Unfortunately, an Israelite woman in the first century did not have the luxury of shopping at her local Ralph's for such a convenience.
To be clear, here is a picture of what not to think of when reading this parable:
Yeast is actually a gas-producing microorganism that we have, with our advanced technology, somehow extracted from nature and neatly packaged in this way for the convenience of the professional baker or modern housewife, so that it could be stored on the shelf or in the refrigerator for immediate use. But all this is recent stuff. It wasn't until Louis Pasteur's findings in the mid-19th century that we even learned what caused fermentation in the first place. Certainly a first-century Israelite woman would not have viewed leaven as little brown granules that came in packets. For her fermentation was something that existed in nature, in the bubbling foam of beer for instance, or when wheat bran was steeped in wine. A messy, smelly and (in my opinion) semi-disgusting phenomenon that looked like this:
The ancients saw the work of leaven as a spontaneous and mysterious thing, perhaps even magical. Quite often yeast spores would simply be floating in the air and land on bread dough that happened to be lying out in the open, naturally causing it to rise. And once you find a source of leaven that you can utilize for your bread making, you save a small lump of the dough as a starter for the next batch. This starter dough may be what the woman in the parable hid in her three pecks of meal.
If you picture the woman hiding her lump of starter dough into a batch that produces two neat little loaves of bread, that doesn't seem like a very impressive example of the "small beginnings, great results" aspect of the kingdom of heaven that Jesus is trying to illustrate. However, once you realize that three pecks of meal equals about 40 liters, which makes enough bread to serve well over one hundred people, the parable makes sense. A small lump of dough hidden in that huge quantity of meal works slowly and steadily to leaven the entire batch, much like the word of the gospel spreads from mouth to mouth and heart to heart until the kingdom of God has increased over the entire world.
Matthew once again reminds us, in dead-horse-beating fashion, that Jesus speaks these parables to confound the multitudes, not necessarily to enlighten them. Psalm 78, from which Matthew quotes, recounts the history of God's faithfulness to Israel despite being continually provoked to anger by their rebellion. It is only fitting that Jesus speaks these parables to the unbelieving multitudes which talk about how God's kingdom will continue to increase like a great tree, or like an enormous quantity of leavening dough, regardless of whether they choose to believe.