Jesus’ Parable of the Leaven is found in two of the Gospels. It is a very simple story—a snapshot of life, really: “The kingdom of heaven is like yeast that a woman took and mixed into a large amount of flour until it worked all through the dough” (Matthew 13:33; cf. Luke 13:20-21).
Jesus uses this 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?
First, it’s important to define “kingdom of heaven.” By this, Jesus is referring to His domain as the Messiah. In the current age, the kingdom of heaven is spiritual, existing within the hearts of believers (Luke 17:21). Later, the kingdom will be manifest physically, when the Lord Jesus establishes His throne on this earth (Revelation 11:15).
In the Parable of the Leaven, we learn several things about the working of the kingdom in our present age. Each of these lessons stems from the nature of yeast.
First, the kingdom of God may have small beginnings, but it will increase. Yeast is microscopic in size, and only a little is kneaded into the dough. Yet, given time, the yeast will spread through all the dough. In the same way, Jesus’ domain started with twelve men in an obscure corner of Galilee, but it has spread throughout the world. The gospel makes progress.
Second, the kingdom of God exerts its influence from within, not from without. Yeast makes dough rise from within. God first changes the heart of a person, and that internal change has external manifestations. The gospel influence in a culture works the same way: Christians within a culture act as agents of change, slowly transforming that culture from within.
Third, the effect of the kingdom of God will be comprehensive. Just as yeast works until the dough has completely risen, the ultimate benefit of the kingdom of God will be worldwide (Psalm 72:19; Daniel 2:35). “The earth will be filled with the knowledge of the glory of the LORD, as the waters cover the sea” (Habakkuk 2:14).
Fourth, although the kingdom of God works invisibly, its effect is evident to all. Yeast does its job slowly, secretly and silently, but no one can deny its effect on bread. The same is true of the work of grace in our hearts.
The nature of yeast is to grow and to change whatever it contacts. When we accept Christ, His grace grows in our hearts and changes us from the inside out. As the gospel transforms lives, it exerts a pervasive influence in the world at large. As we “reflect the Lord’s glory, [we] are being transformed into his likeness with ever-increasing glory, which comes from the Lord, who is the Spirit” (2 Corinthians 3:18).