In today’s Gospel from St. Matthew, Jesus offers three parables to help the crowds understand the kingdom of heaven: The kingdom of heaven is like a man who sowed good seed in his field. The kingdom of heaven is like a mustard seed that a person took and sowed in a field. The kingdom of heaven is like yeast that a woman took and mixed with flour until the whole batch was leavened.
The one of the three parables that resonates the most with me is that of the yeast. Doubtless that is because we bake bread with regularity. I’ve seen the “magic” of mixing a few teaspoons of leaven into water and flour and seeing it turn into a beautifully risen dough. Here is St. Maximus of Turin’s explanation of the power and characteristics of leaven:
For although it is small in size, simple in appearance, and common in nature, it has such power within it that, when it has been concealed in flour, by its inherent energy it makes the whole mass what it itself is. And it so diffuses itself throughout the lump by the force of its spreading that it causes the whole mass of flour to become leaven, and thus the thing itself, by is own power, acquires for itself a mass that shares its own strength.
Maximus explains Jesus’ use of that parable this way: The leaven is compared to Jesus
who, when He was a man in form, little in humility, and cast down in weakness, was interiorly so powerful [that] when He began to spread Himself about through the whole earth by the power of His divinity, He immediately drew the entire human race into His substance by His own strength…He made it possible for everyone to be what He Himself was.
Sometimes when I have read that parable, I think of our job as being the yeast for others. But as I read this, it seems to me more accurate to say that our job is to help activate the yeast that already exists in all of us.
Jesus has already drawn all into His substance. Our much simpler job is to simply (a) realize that for ourselves and (b) help others to realize it about themselves.
Go forth and activate that yeast.
Creo en Dios! 
When I asked the folks who God was, they said “God is the leaven. We have to knead the world.”