Yeast is known world-wide.  It is used in brewing, to convert sugars into alcohol; and in baking, to produce carbon dioxide which lightens or ‘leavens’ the texture of bread.  Yeast cells grow at an amazing rate, budding off ‘daughter cells’ which also grow and bud.  It only requires a little yeast in the right growing conditions to eventually produce millions of yeast cells which have a powerfully increased effect.  

In the Old Testament, when God brought His people out of Egypt to start their wilderness journey to the Promised Land, He told them to take bread that had no yeast.  That ‘unleavened’ bread would not go bad quickly.  Every Passover festival (which celebrates God’s deliverance), each household was to clean their houses for seven days to ensure there was no yeast (Exodus 12:17-20).  Yeast is a picture of sin which multiplies and gets everywhere unless it is rooted out (1 Corinthians 5:6-8).

Paul used yeast as an illustration to show how easily false teaching (verbal encouragements to sin by failing to honour God’s instructions) can spread through a church and change it (1 Corinthians 5:6).  The particular wrong teaching was that circumcision was essential if Christians were to be accepted by God.  It had spread like yeast.  But Paul was persecuted harshly for saying that their teaching was wrong – as Jesus was hated for condemning the teaching of the Pharisees (Mark 8:15).  False teaching is not only dangerous for people who hear and follow the lies - it brings the penalty of God’s judgement to the people who are spreading the lies.  However sincere they may be: if they are wrong, God holds them accountable.
 
The only way to identify and eliminate false teaching is to know the truth; then the lies can be rejected.  That was why Paul spent so much time in this letter explaining which teachings are true and which are false.  The Bible continues to give us God’s standard for truth in every area of life and doctrine.  That is why Word@Work is produced, to enable Christians all over the world to choose to embrace the truth and reject the lies.  So each of us need to be constantly alert and not naïve; the devil is called the ‘father of lies’ (John 8:44) and he continues to ensure that they are spread everywhere, including where you are today.