I made a few changes/improvements on 3/22 (including a new, spicier title).
The following is a piece I wrote on the parsha for my school's "Parsha Press":
The entire second perek of Sefer Vayikra discusses the laws of menachot, flour offerings. In verses 11 through 13 the Torah presents some general halachot of menachot. I will focus on some of the ideas expressed in verse 11:
11. Any meal offering that you offer to Hashem do not make chametz (leavened): for all leavening and fruit-honey, you may not offer/burn from it an isheh laHashem (fire-offering to Hashem).
The following is a summary of the halachot the Rabbis derive from this verse:
1) No offerings may be brought with chametz.
2) No offerings may be brought with fruit-honey.
What is the reason for these prohibitions? The Rambam maintains that the ta'am, reason, for most of the practices associated with korbanot, as well as many other mitzvot, is the Torah's desire to distance us from the practices of the idolaters. In the Moreh Nevuchim (III:46) he explains that the idolaters would use chametz and fruit-honey in their offerings to their gods. We do not do so - because we wish to distance ourselves from their practices. Additionally, the Rambam explains, this explains why korbanot (Vayikra 2:13) must be offered with salt: because the idolaters never used salt.
The Ralbag writes in his "Toelot" (meaning, lessons - in which he explains the lessons of each section of the Chumash) that he agrees with the ta'am given by the Rambam but he also gives another reason that is more particular to this case. I will paraphrase the Ralbag's comments: The ancients (before the Torah was given) believed that nature was random and they did not recognize that there is a Creator and everything has a cause. Because of this belief they thought that the products of their own craft were greater than anything in the natural world. Chametz and fruit-honey are artificial - they do not occur naturally. The Torah wants us to bring korbanot from our best products. Therefore, the Torah prohibits these artificial products to emphasize the superiority of the natural products of Hashem's Creation.
I believe the Ralbag's idea might help explain why the idolaters used chametz and fruit-honey in their offerings. The idolater serves his god as a means to furthering his own designs, dreams and aspirations. He hopes that by currying favor with his god he will gain success. Sacrifice, for an idolater, is an opportunity to impress his deity - so, of course, he gives what he believes is the most impressive fruits of his labor (man-made products). The Torah has the exact opposite intention - the offering of korbanot is an opportunity for the oveid Hashem to submit himself to Hashem and marvel at the beauty of His Creation. Hashem can not be impressed by our gifts. In other words, in the man-centered universe of the idolater the artificial is what is most impressive - in the G-d-centered universe of the Torah the artificial is only a distraction to recognizing the ultimate Wisdom of G-d's Creation.
One last thing should be mentioned. When the Rishonim or other Rabbis offer ta'amim for the chukei haTorah they are not attempting to give the reason for the mitzvah they are only attempting to give a reason. And it is imperative to seek these reasons. To paraphrase the Rambam at the end of Hilchot Temura (see also the end of Hilchot Meilah): Even though all the chukei haTorah [the korbanot are chukim] are g'zeirot (decrees) we must contemplate them - and for whatever you are able to give a ta'am (reason), do so.
For further thought: Is there a connection between this chametz prohibition and the prohibition of chametz on Pesach?