What struck me as a little strange is how did the "positive commandment" notion of eating matzah become such a strict prohibition against eating chametz, so strict that even possessing chametz earns you "kares", your soul being cut off from your people (whatever that means).
It seems slightly weird. Why eliminate all chametz, instead of just adding a commandment to make sure you eat Matzah. My wife speculated that perhaps to heighten the experience of eating Matzah only, you need to enforce total eradication of chametz. I can kind of buy that argument, though it seems that the punishment is still disproportionate. Why get rid of all the chametz? Why not just say, don't eat it for a week.