I wrote on this passage when we came across it in Matthew (the same illustration is used twice, though probably on different occasions).
The more I look at it, however, I wonder if perhaps Jesus didn’t mean something else than what I first said. Knowing Jesus and how he often uses multiple meanings for the same illustration (Matthew 5:23-26 and Luke 12:54-59 for example), perhaps he meant more than one thing.
But I feel I would be remiss if I didn’t mention this possibility because it is a very important one. Jesus said,
What shall I compare the kingdom of God to? It is like yeast that a woman took and mixed into a large amount of flour until it worked all through the dough. (20-21)
If there is one consistent picture throughout the Old Testament, it is the idea of yeast and impurity or sin. One of the pictures of the Passover meal was the unleavened bread. What happened to that bread? It was broken and eaten, giving (physical) life to those who ate.
Why was it unleavened? There was, of course, the practicality of the matter. The Jews had to prepare to leave Egypt quickly, and so God told them to cook bread without yeast as it would bake faster.
But there is another very important reason. Jesus called himself, “The bread of life.” And later, at the Passover meal, Jesus took the bread and broke it, saying, “This is my body given for you.” (Luke 22:19)
When Jesus died on the cross, he didn’t do so for any sin he had committed. Like the Passover bread, he was completely free of impurity or sin. But his body was broken for our sins. He took our sins upon himself and took the punishment for our sins. And now, if we eat of this living bread, in other words, if we believe in him and put our faith in his work on the cross, we will have eternal life.
But getting back to the point, yeast is always used as a picture of sin and impurity. Yet here, Jesus uses the picture of yeast spreading throughout bread to illustrate the kingdom of God?
Why? The answer is scary. It is very possible for corruption to spread among God’s people.
You don’t believe me? Just look at what’s happening in America today. The Episcopal church started allowing gay marriages last year, and just this past week, the Presbyterian church allowed the same.
That’s just the moral side.
Throughout the centuries, we’ve seen corruption come into the church in terms of who Christ is. You have people disclaiming the virgin birth, the resurrection of Christ, and his deity, all the while claiming to be Christians.
How can they do this? By discrediting the very word of God. And of course, by discrediting the Word of God, it becomes easy for moral corruption to creep into the church as well.
Jesus warned us about this. He talked about Satan sowing weeds among the wheat. Among the evil that Satan plants in the world is the false doctrine that he also spreads within the church itself. (Matthew 13:24-30, 36-43)
And Jesus warns in the latter part of this passage of people who claim to know Christ, but don’t. So he tells us,
Make every effort to enter through the narrow door, because many, I tell you, will try to enter and will not be able to. (24)
What is my point? Be watchful. Be careful of what your pastors are saying. Be careful of the people you listen to on podcasts or on the radio. Be careful of what you read. If what you hear and read is consistent with God’s word, accept it and obey it. If not, reject it. If you’re not watchful, corruption can easily spread into your hearts and minds.
So as the apostle Paul wrote,
Test everything. Hold on to the good. (I Thessalonians 5:21)