If there was one book I wish I could have given to every pastor I met in South Africa [and I’ve sent one to Attie], Klyne Snodgrass’ new book, Stories with Intent, is the one. Why? Because we need more preaching on the parables, and because this book delivers the goods on the parables — nothing fancy, nothing adventurous, nothing controversial — just solid, commonsensical study of the parables of Jesus in his world. And, yes, if I were a pastor this book might in itself generate a series of sermons on the parables.
This parable should strengthen the resolve of each of us in two ways: that God is at work in Jesus, regardless of what it looks like, and the little work we do is actually the large work of God in our world.
Our parable today? The Mustard Seed. Here it is in Matthew 13:33 and then Luke 13:20-21:

He told them still another parable: ?The kingdom of heaven is like yeast that a woman took and mixed [hid] into a large amount of flour until it worked all through the dough.?

Again he asked, ?What shall I compare the kingdom of God to? 21 It is like yeast that a woman took and mixed into a large amount of flour until it worked all through the dough.?

Klyne observes that the word “hid,” Snodgrass suggests, is unusual and evocative of the hiddenness of the kingdom.
Culturally, “leaven” (which is not the same as “yeast”) was seen negatively — think of the need to purge the home of leaven for Passover. Leaven is fermenting dough; yeast is that which causes the leavening. And, yes, one of the typical tasks done by women was working dough. Finally, it should be observed that the amounts given in the Gospels, if understood typically, would be enough bread for 100-150 people.
A feature of this commentary is a sketch of the options in interpretation, including the allegorical ideas of the ancient church. Here are some more modern options: God’s power now present; contrast of present with future; negative feature of leaven leads to Jesus as subversive; the hidden pervasive force of the kingdom; women in leadership.
We need to be careful to read too much of the Mustard Seed into the Leaven parable.
Big point: yes, leaven often occurs negatively; but the context reveals the negative element. There is nothing negative here. The point then: as leaven ferments dough, so Jesus’ kingdom ferments in his world.
Once again, Jesus’ ministry is not what folks thought a messianic ministry would be. His ministry was too hidden but there is a discernible presence — and it is at work.