Matthew 13:33 (HCSB)
"He told them another parable: "The kingdom of heaven is like yeast that a woman took and mixed into 50 pounds of flour until it spread through all of it."
Reading different commentators on this one there is a range of thought on what Jesus is saying here. Some take the position that yeast is representing sin spreading in the church. It is true that in many other passages yeast is used to describe the way sin or bad things spread, but I don't see the yeast being a bad thing here.
In this parable the woman put yeast into the flour on purpose. She then mixed it into the flour on purpose. I think she wanted the yeast to spread throughout the flour and change it. And it did. It was a good thing. The kingdom of heaven is like that yeast. Jesus shared the message of the good news of the kingdom of heaven, and the reign of God has been spreading through the world ever since. At a personal level, I sense the reign of God growing in my life as well.
I pray that God's kingdom come, that His will be done, here on earth as it is in heaven. I pray His reign will be evident in my life, and that His rule would continue to spread in my life and in the world around us.