How does God's kingdom grow on earth as It Is In heaven? What do mustard seeds and yeast have to do with it? Matthew 13:31-35

The Parables of the Mustard Seed and the Yeast

31 He told them another parable: “The kingdom of heaven is like a mustard seed, which a man took and planted in his field. 

Jesus again uses the metaphor of a seed, but this time in a different way.  Remember in parables we don't try to analyze and give meaning to every single, small detail but the story as a whole.  Some people get caught up in the fact that some have found seeds smaller than the mustard seed, and it causes them to doubt the bible's truthfulness.  This is the problem with taking a literal view of the bible when it is clearly meant not to be taken literally by the context.   

32 Though it is the smallest of all seeds, yet when it grows, it is the largest of garden plants and becomes a tree, so that the birds come and perch in its branches.”

The purpose of the parable is to teach yet another aspect of how God's kingdom works here on earth.  The main point is that though something may seem very small in the world's eyes, when it is put to use for God's kingdom it produces something supernatural.  

"The mustard plant customarily never grows beyond what one would call a bush, and at its normal size would be an unlikely place for bird’s nests. The tree-like growth from this mustard seed describes something unnatural. (i..e it can't be explained in human terms)" Guzik

“Not in nature but in size; an excusable exaggeration in a popular discourse…it serves admirably to express the thought of a growth beyond expectation. Who would expect so tiny a seed to produce such a large herb, a monster in the garden?” (Bruce)

33 He told them still another parable: “The kingdom of heaven is like yeast that a woman took and mixed into about sixty pounds of flour until it worked all through the dough.”

Jesus uses another familiar process that would be known in his culture, the making of bread.  The same message is baked into this parable (haha!).  The idea being that a small amout of leaven works through a huge batch of dough.  Though it is small, it has a large and significant influence on the end product.

This was an unusually large amount of meal. It was much more than any normal woman would prepare, and again suggests the idea of massive or unnatural size. Guzik

i. “Three measures of meal would be about 40 litres, which would make enough bread for a meal for 100 people, a remarkable baking for an ordinary woman.” (France)

Ordinarily leaven is seen as a bad thing in the Jewish faith.  I.e. Galatians 5:9 "A little leaven works through the whole dough." The represented false teaching i.e. the legalism that cropped up in the Galatian church.  Also, the Jews ate unleavened bread as a sign of obedience to God.  

"The kingdom of heaven is like leaven.’ Now of course, leaven is generally in Scripture taken as a symbol of evil or corruption. For example, the preliminary to the Passover Feast was the purging of the houses of the Israelites of every scrap of evil ferment, and the bread which was eaten on that Feast was prescribed to be unleavened. But fermentation works ennobling as well as corruption, and our Lord lays hold upon the other possible use of the metaphor." MacLaren

34 Jesus spoke all these things to the crowd in parables; he did not say anything to them without using a parable. 

It wasn't as if Jesus was intentionally trying to hide or keep things a secret from the crowds, but he used parables as a way to sift out those who were there only to watch a show and weren't really serious about who Jesus was or what he taught.  It doesn't mean he never spoke in anything but a parable, but he also used parables because of the growing faction of the Jewish leaders, who were plotting against him.  

"The words are, of course, limited by the context to this occasion, but it is noticeable from this time forward that parables are the dominant element in His teaching to the multitude, and that the mysteries of the kingdom are reserved for the more esoteric instruction of the disciples." (Ellicott)

35 So was fulfilled what was spoken through the prophet: “I will open my mouth in parables I will utter things hidden since the creation of the world.”

This quotation is from Psalm 78:2.  It reminds us that there was a prophetic element in many of the psalms.  I.e. Psalm 69:8 - Messiah would be rejected by his people. Psalm 8:2 - Messiah would be praised by little children.  Psalm 69:2 - Jesus would be offered vinegar to drink.  Psalm 22 has many Messianic prophecies, including the famous "My God, my God why have you forsaken me. "  22:1

In summary, the two parables illustrate two lessons about God's kingdom. 

1. The mustard seed which grew into a huge tree which provided a huge nest for birds represents the growth in quantity of the kingdom.  Many think it is a reference of the growth of the church after Jesus died and rose again.  With the seed of the gospel the church grew to reach many people of all different cultures. 

2. The leaven produced a qualitative effect on a huge amount of dough.  Many think this is analagous to the Christian influence on the world around it.  Instead of enabling corruption like the false teachers, it could influence the world for good.  This is why Jesus teaches on the Sermon on the Mount for the church to be the salt and light of the world.  Salt like leaven needed to be worked through all of the meat so it could have its effect on the meat to keep it from rotting.  

Where is God calling you to have a mustard of faith, which God could use to grow his kingdom?  What small step of faith can you take to be obedient to what God is calling you to do?  Does your life have a leavening effect on those around you in a good way?  I.e. When you are in a situation social or otherwise do you bring God's grace and goodness into it.  Do you flavor the conversation with words and stories reflect godliness vs. worldliness?  Do you mix in with the crowd to be like everybody else or do you walk in the Spirit to be the man or woman God wants you to be?