From the second perek of Vayikra:
seor, sourdough, is what causes bread to rise. But it can rise without it, just from the natural bacteria occurring in air, which is why after some estimate of time (such as 18 minutes or 40 minutes) we must be concerned lest matzah became chametz, or if it shows signs of chimutz.
But here, what is being prohibited? One could read the pasuk on a literal level that practically no meal offering will be chametz, because (ki) the ingredient they add deliberately to get good chimutz, namely sourdough, may not smoke as an offering by fire to Hashem. But that would not preclude naturally occurring limited chametz.
The alternative is the opposite, that there is a general prohibition of chametz which holds true. The reason might be seor, but it applies even without the seor; or the whole mention of seor is flowery language and repetition. What do you think about the merits of interpreting this pasuk in either direction?