One of the satisfying moments in baking is seeing how much a lump of dough has risen, filling its bowl.  A child seeing this for the first time exclaims, "Your dough has grown!"  

The dough expanded, yes.  It has not grown in substance.  There is no more dough in the bowl than there was two hours before.  If you look on your yeast package, you will find 0 calories in yeast.  

Leaven puffs up.  It is an apt symbol for human sinfulness.  Our pride puffs us up, makes us think of ourselves as better than our neighbor.  Yet not a single one of us is made more in the image of God than our neighbor.

In Matthew 16, Jesus tells His disciples, “Beware of the leaven of the Pharisees and Sadducees.”  In the Old Testament, because leaven is a potent symbol (beginning in Exodus 12), Jewish rituals involved sweeping out every ounce of leaven from the house for various festivals.  For the feast of unleavened bread, for example, Moses said, “No leaven shall be seen with you in all your territory.”  Jewish children grew up hunting the floors for the last crumb that could be leavened.

So, when Jesus told His disciples to beware leaven, they seem to have, at first, taken Him literally.  It was only when He explained, “Then they understood that he did not tell them to beware of the leaven of bread, but of the teaching of the Pharisees and Sadducees” (Matthew 16:12).

The Pharisees and Sadducees were both teaching from the Bible and from holy rituals started by Moses.  But the way they taught did not humble their listeners.  Instead, it made them proud (see Luke 18:11).

Teaching that seems Biblical and makes us feel good about ourselves is popular in our part of the world.  It looks like growth.

On the other hand, Jesus’ teaching can be hard to grasp at first (Matthew 16:5-11, 21-23).  He lays on us a humility that comes in bearing a cross (Matthew 16:24-28).  We may well feel much smaller than our neighbors.

But what is added to us through the teachings of Christ is the very Spirit of God.  Peter said, “Lord, to whom shall we go?  You have the words eternal life” (John 6:68).  And Jesus has a promise for the one who hears His word and feels poor or weak.  “Blessed are the meek, for they shall inherit the earth.  Blessed are those who hunger and thirst for righteousness, for they shall be satisfied” (Matthew 5:5-6).

Keep at the task of reading through the New Testament.  I’m glad to answer any questions you have.  If the Apostles had questions, we certainly will, too.  God bless you!