Parable of the Leaven (Yeast)

The parable of the Leaven (also called the Parable of the yeast) is one of the shortest parables of Jesus Christ. It appears in Matthew 13:33 and Luke 13:20-21. In both verses and nooks, it immediately follows the parable of the Mustard seed, which shares this parable's theme of the kingdom of heaven growing from small humble beginnings.

Matthew 13:33 New Living Translation (NLT)

Parable of the Yeast
33 Jesus also used this illustration: “The Kingdom of Heaven is like the yeast a woman used in making bread. Even though she put only a little yeast in three measures of flour, it permeated every part of the dough

The parable describes what happens when a woman adds leaven (fermented old dough usually containing lactobacillus and yeast) to a large quantity of flour. The living organisms in the leaven grow overnight, so that by morning the entire quantity of the dough becomes affected.

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In the Gospel of Luke, the parable is as follows:

Luke 13:20–21, English Standard Version

And again he said, “To what shall I compare the kingdom of God? It is like leaven that a woman took and hid in three measures of flour, until it was all leavened.”

This parable is part of a pair and shares the meaning of the preceding parable of the mustard seed emphasizing on the powerful growth of the kingdom of God from small beginnings. The final outcome is inevitable once the natural growth process has begun.
The picture of a woman making bread with leaven, portrays the reality of Gods kingdom and the point of comparison is the powerful growth of the kingdom from small beginnings.
In essence, we have to believe and trust the growth process of our little humble beginning.

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Although, leaven symbolizes evil influences elsewhere in the New Testament ( Luke 12:1). It is generally not interpreted that way in this parable.

As with the parable of the lost coin, this parable is part of a pair whose first parable describes the works of Jesus Christ in terms of agricultural activities of men in comparison to Tue second parable with a focus on women's domestic activities.
The quantity of flour though large, may hint a planned festive occasion since the bread produced could feed multitude of people. Three measures of the flour was equivalent to the amount used by Sarah to band bread when she and Abram paid a visit to Melchizedek and the angels.

Jesus' parable of the leaven is a succinct story with a reality comparison as the kingdom is likened to yeast that a woman took and mixed into a large amount of flour until it pulled through into a dough.
Jesus uses the story as an object lesson to illustrate the kingdom of heaven.
A woman takes yeast (leaven) and mixes it into dough. Eventually, the whole of the dough is leavened. What does it mean?

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Firstly, the kingdom of heaven here describes the reign of the Messiah. In the current age, the kingdom if heaven is spiritual existing within the hearts of the believers (Luke 17:21).
Afterwards, the kingdom will manifest physically when the Lord establishes his throne on Earth.
(Revelation 11:15).
Yeast grows and changes whatever it contacts. When we accept Jesus Christ as our Lord and saviour, his grace grows within our hearts and alters within and outside. The gospel transforms lives and exerts a pervasive influence globally.
The effect of the kingdom of God is comprehensive and exerts a greater impact on humanity. The ultimate benefit of the Kingdom of God is global just as Yeast works until the dough has completely risen.

Habakkuk 2:14

“The earth will be filled with the knowledge of the glory of the LORD, as the waters cover the sea”

Although, the kingdom of God works invisibly, it's effect is evident to us all. Yeast does it job slowly but steadily yet it is silent but effective. It's effects on bread is pronounced.
The same is true of the work of grace in our hearts.