Pesach - Matzah
The Matzah and Chametz are really very similar. In fact they have almost the exact same ingredients. It is basically flour and water.
Yet, one is a mitzvah to eat on Pesach, and one is assur to eat on Pesach. One is the symbol of freedom from the slavery of Egypt and one is not. One is the bread of the poor man and one is the bread of the wealthy. One costs 6 NIS in the store to buy and one costs upwards of 160NIS per kilo.
The difference between these two items that are really so similar is striking.
This teaches us a lesson that it is all a matter of what you do with it. You can have a character trait, for example, that can go either way. It can be used for good or for bad. It is a matter of your attitude and your direction.
You can take the flour and water and make it into chametz, you can take the flour and water and make it into matzah. You can take any character trait within you, any behavioral custom, and use it for good, or use it for bad.
Matzah is not good or bad and chametz is not good or bad. But the same item can be used to make one or the other. The lesson of the matzah is that just like we have to purge the chametz from within us, so too do we have to learn to use our behaviors and traits for good and not for bad.