leaven: a lump of fermenting sourdough kept from an earlier baking and worked into fresh dough to make it rise, used in the New Testament as a picture of a small, hidden influence that spreads through and changes a whole mass.
In the ancient world leaven was not the packaged yeast we buy today. It was a lump of sour, fermenting dough held back from an earlier baking and kneaded into a fresh batch, where it slowly worked its way through the whole and made it rise. That physical picture, small and hidden and quietly spreading until nothing is untouched, is what every New Testament use draws on.
Most of the time the picture is a warning. Israel's Passover called for every scrap of leavened food (חָמֵץ) and every bit of starter (שְׂאֹר) to be hunted out and thrown away, so for many first-century readers the word already carried the sense of something that corrupts and must be purged. The three settings where it appears fall into a clear pattern:
- In the Gospels it is the corrupting influence of others you must guard against, the "leaven of the Pharisees."
- In Paul's letters it is an evil already inside the community that must be cleared out before it spreads.
- In one parable, surprisingly, it is the kingdom of God itself.
That last use is the puzzle. When Jesus compares God's reign to leaven a woman hides in a great batch of flour until all of it is raised, he takes an image his hearers were trained to distrust and applies it to something good. Interpreters have argued for over a century about whether he simply borrowed leaven's physical trait, a tiny hidden agent that transforms everything, or deliberately chose a shocking image to say God's reign shows up where respectable religion would least expect it. Both readings are defended by serious scholars, and the parable's force may come from the tension itself.
Nuances
Whether the parable uses leaven as a straightforwardly positive image (a tiny hidden agent producing a huge result) or deliberately keeps leaven's usual negative charge, so that the kingdom is pictured under the guise of something unclean.
- majorityA positive image: leaven simply illustrates how the kingdom starts small and hidden yet works through everything until the whole is transformed. The point is the contrast between the tiny agent and the immense result.; Klyne R. Snodgrass, Stories with Intent (2008), 226-235; Joachim Jeremias, The Parables of Jesus, 3rd rev. ed. (1972), 146-149; R. T. France, The Gospel of Matthew (NICNT, 2007), 528; W. D. Davies and Dale C. Allison, Matthew (ICC, 1988-1997), 2:420-424
- minorityA deliberately shocking image: because leaven almost always signaled corruption and was purged at Passover, Jesus's comparison is startling on purpose, locating God's reign in what convention treats as unclean and hidden.; Robert W. Funk, "Beyond Criticism in Quest of Literacy: The Parable of the Leaven," Interpretation 25 (1971): 149-170; Bernard Brandon Scott, Hear Then the Parable (1989), 321-329; John Dominic Crossan, In Parables (1973)