1 Corinthians 5:7

1 Corinthians 5:7 - Get rid of the old yeast that you may be a new batch without yeast - as you really are. For Christ, our Passover lamb, has been sacrificed.

In this verse Paul uses bread and yeast to represent our lives. When the Israelites celebrate Passover they make all their bread without yeast. Yeast represented sin and when the lamb was sacrificed it was so that their sin would be covered by the blood. So as a representation of a sin free life they prepared everything without yeast.
What we must understand about yeast is that it doesn't take much. Just a pinch will work itself through the whole batch of dough. It may not be evident at first, but before you know it the yeast has exploded and it becomes visible to everyone who sees it that there is yeast in the dough.
That is how it is with sin as well. It doesn't take much, just one small compromise and it starts. Before you know it sin has crept back into every area of your life. You may be able to hide it at first, but it will eventually become so big that everyone will know it is there.
In order to prevent this we must follow the instructions in this verse. Get rid of the old yeast, that you may be a new batch without yeast! That is who you really are!
Christ has been sacrificed and through Him we are made new, without sin. Now we must get all the old out. If you do not do this it will creep back in. Don’t let that happen. Be proactive and stop the sin before it starts - seek God and put Him first in every area of your life.