The Five Gospels compares Luke 13:20-21 with Matthew 13:33 and Thomas 96:1-2. Here is the commentary that follows the passages in Matthew and Luke.
Ginny
Matthew 13:33He told them another parable: Heaven's imperial rule is like leaven which a woman took and concealed in fifty pounds of flour until it was all leavened.
Leaven. This parable transmits the voice of Jesus as clearly as any ancient record can, in the judgment of most Fellows of the Jesus Seminar.
In this one-sentence parable, Jesus employs three images in ways that would have been striking to his audience. The woman takes leaven and "conceals" it in flour. "Hiding" leaven in flour is an unusual way to express the idea of mixing yeast and flour. The surprise increases when Jesus notes that there were "fifty pounds" of flour. Three men appear to Abraham in Genesis 18 as representatives of God. They promise him and his wife, Sarah, that she will bear a son the following spring, although she was beyond the age of childbearing. For the occasion, Sarah is instructed to make cakes of fifty pounds of flour to give to the heavenly visitors. Fifty pounds of flour, it seems, is a suitable quantity to celebrate an epiphany--a visible, though indirect, manifestation of God. The third surprising figure in the one-line parable is the use of leaven.
Jesus employs the image of the leaven in a highly provocative way. In Passover observance, Judeans regarded leaven as a symbol of corruption, while the lack of leaven stood for what was holy. In a surprising reversal of the customary associations, the leaven here represents not what is corrupt and unholy, but God's imperial rule--a strategy the Fellows believe to be typical of Jesus.
Luke 13:20-21He continued: What does God's imperial rule remind me of? It is like leaven which a woman took and concealed in fifty pounds of flour until it was all leavened.
Leaven. Like the mustard seed, the parable of the leaven makes light of an established symbol. Leaven was customarily regarded as a symbol for corruption and evil. Jesus here employs it in a positive sense. That makes his use of the image striking and provocative.
The mustard seed and the leaven are picture parables: they paint a simple but arresting picture that depends, for its cogency, on the juxtaposition of contrary images. To compare God's imperial rule to leaven is to compare it to something corrupt and unholy, just the opposite of what God's rule is supposed to be. This reversal appears to be characteristic of several of Jesus' sayings, such as "the last will be first and the first last." The Fellows included the parable of the leaven in that small group of sayings and parables that almost certainly originate with Jesus.