The single instance of a positive view of leavened bread in the Scriptures is the parable of the yeast:
He spoke to them another parable. "The kingdom of heaven is like yeast that a woman took and mixed with three measures of wheat flour until the whole batch was leavened." Matthew 13:33
The usual interpretation of the parable is similar to that given for the parable of the mustard seed: that the kingdom of God starts out small and seemingly insignificant, but eventually grows in importance. However, some commentators have suggested that the parables are much more radical, even subversive. In this view, a parable’s purpose is to challenge the religious status quo, such that the core meaning of most of the parables is: “God is not like you thought.” The parable of the yeast would have been especially disturbing to his first century audience. All three of the elements of the analogy---the yeast, the woman, and the amount of flour---would have challenged the theological common sense of the day.
We have already seen how yeast was often considered a symbol of corruption and decay in Jewish tradition, so it would have been shocking for Jesus’ audience to hear the kingdom of God to be compared to yeast. His implication seems to be that the new principles of the kingdom of God will challenge traditional views about what is pleasing to God. As we have seen, the Beatitudes and the rest of the Sermon on the Mount seem to bear this out. Jesus calls the poor, the sorrowful, and the persecuted “blessed,” a designation that would have been counter-intuitive for people who were taught that God rewarded the virtuous with material prosperity. Jesus also establishes new principles for discipleship and holiness that go beyond the previous standards of the Mosaic Law. He often prefixed his discussion of a traditional teaching with “You have heard it said . . .” followed by a more demanding precept of right living. Jesus’ association with sinners and fishermen instead of scribes and Pharisees was a clear sign that the kingdom of God that he announced was going to shake things up.
The second surprise of the parable was the analogy of the activity of God being compared with the homely tasks of a woman. Women in first century Jewish society may have been better off than in some other cultures of the ancient world, but they were still second-rate citizens, considered weak, prone to sin, and in need of the guidance and protection of a father or husband. Throughout the gospels, Jesus is portrayed as treating women with extraordinary respect and compassion. But the parable goes further in depicting the woman as an agent of the kingdom, in her own sphere of influence. This more positive view of women is expressed most fully in Galatians 3:28: “There is neither Jew nor Greek, there is neither slave nor free person, there is not male or female, for you are all one in Christ Jesus.”
The amount of flour is the most surprising element of the parable, which is not entirely evident in most English translations. “Three measures” is the usual translation for the original Greek “tria sata” which is a little over a bushel of flour (1.125 bushels, to be precise). That’s a ridiculously large amount of flour---you’d need a 100-quart Hobart mixer with a dough hook as big as your leg to knead it! Translating into kitchen measures, 1.125 bushels is 144 cups of flour. Presuming we used a common recipe for basic white bread that uses 5 ½ cups of flour, 144 cups is enough to make 26 batches of bread of two loaves each, giving us a total of 52 loaves, each weighing about a pound and a half. If we’re frugal but not stingy, we can get 16 slices out of a loaf, yielding 832 slices, enough for 416 peanut butter and jelly sandwiches (we’d need 33 jars of jelly, and 64 of peanut butter).
What’s the message of the story? It’s simple: The kingdom of heaven is like a woman who wants to do more than feed her family. The kingdom announced by Jesus is like a woman who wants to feed the village. The kingdom of God is like a woman who wants to feed the world. The kingdom is for everybody.
 For a more complete analysis of the parables as radical stories, see Parables as Subversive Speech: Jesus as Pedagogue of the Oppressed, William R. Herzog II (Westminster/John Knox Press, Louisville, KY 1994).
 Although other commentators have written similar analyses, my first encounter with such an interpretation of the parable of the yeast was in “Preaching the Parables of Jesus” (Church, Winter 1992; pp. 19-24) by Dr. Richard Stern.