Chametz on Pesach has its own unique category of stringency, we clean everything and everywhere, we have separate pesach dishes and we go after every last piece with no exceptions.

 Why so extreme?

This can be explained by understanding what the Zohar says about Matzah. Matzha is called "Lechem De'mheymenusah" Bread of Emunah, how exactly is Matzah the "bread of faith"?

  

One of the reasons for not eating Chametz on Pesach is because Hashem rushed  Bnei Yiroel out of Egypt not leaving them enough time to bake chametz bread for the way. Instead of letting the bread rise and become Chametz they had to quickly toss it into the oven to get it baked before they left- leaving them with chametz free bread.

Bnei Yisroel spent hundreds of years in Egypt, just a few more minutes is all they needed to prepare some bread for the way. The slavery was already over, what damage would there be in letting them stay a mere few more minutes to bake some fresh Chametz bread?

The message here is very strong and simple, they did not leave Egypt on their own, they couldn't and therefore could not "choose" to stay a few more minutes!!!

Just as Hashem put them there he took them out. In order for this message to never be forgotten,so that in some future generation no one should come along and say the Jews freed themselves, they had 600,000 strong able bodied men and they broke free.

That's why the rush was necessary, to show we did not decide, rather Hashem decided when and how we would leave.

We eat the Matzah because they ate Matzah and we are reminded that they couldn't even "choose" to bake their own bread the way they wanted to. They were entirely dependent on Hashem.

Every time we bite into the Matzah we are reminded of the miracles of Yetzias Mitzraim, we are reminded that  Hashem runs the world and we are entirely in his loving hands. He and only he freed us.

This message gets ingrained over a period of seven days, over and over again with every bite into the "bread of Faith"  which comes to remind us that Hashem is in control, he took us out of Egypt with miracles and he alone runs the world.-  he loves us like a father loves his child.

Eating Matzah and refraining from Chametz over Pesach is to remind us and to ingrain these ideas and truths so that they become a part of us and we should live by them through out the year.