(17) You shall bring from your settlements two loaves of bread as an elevation offering; each shall be made of two-tenths of a measure of choice flour, baked after leavening, as first fruits to ה׳. (18) With the bread you shall present, as burnt offerings to ה׳, seven yearling lambs without blemish, one bull of the herd, and two rams, with their meal offerings and libations, an offering by fire of pleasing odor to ה׳. (19) You shall also offer one he-goat as a sin offering and two yearling lambs as a sacrifice of well-being. (20) The priest shall elevate these—the two lambs*—the two lambs— Force of Heb. construction uncertain. —together with the bread of first fruits as an elevation offering before ה׳; they shall be holy to ה׳, for the priest. (21) On that same day you shall hold a celebration; it shall be a sacred occasion for you; you shall not work at your occupations. This is a law for all time in all your settlements, throughout the ages.
It is now possible to understand why on Pesach we specifically we eat Matzah and on Shavuot we eat Chametz for the two loaves are specifically from chametz. We can say this by way of a hinting in that Chametz is the product of humans. It comes through an earthly awakening. This is alluded to in the Midrash where a wicked person asks one of the sages about the ridiculousness of circumcision. How is it possible that the work of a human is more pleasant than God's creation. He brought in wheat and then a baked product and asked, which one do you think is nicer? From this, we learn that the refined product, something chametzdik, is the product of human hands and results from earthly activation, which for our purposes comes through Torah, mitzvot, and good deeds.
Matzah on the other hand alludes to divine activation. That's why on Pesach, we eat matzah, as it alludes to God's redemption of us, separate of our own actions. On Shavuot, a time for purification of materiality and then revelation of the Torah, we then merit to have the ability to activate the lower and upper worlds. That's why specifically we need chametz, food of humans to tell us that everything depends on us. In doing so, we spread the bounty through all the worlds through our doing mitzvot, Torah, and good deeds and then we can have the sitra achra submit to us until it's finished and we have broken all our wayward attributes and evil desires.
As for the omer offering and the two-loaves offering, the omer is brought from barley, which is the food of animals, whereas the two loaves are the food of man.
The idea is that bread is faith, as written in the Zohar… and the offering of the meal-offering is [a display of] faith and submission to God, may He be blessed, announcing that all is His.
Behold, at the beginning of the exodus from Egypt, it is written: "Yet you were naked and bare" (Yechezkel 16:7), and there was submission because of their low level, and for this reason the omer is the food of animals. Afterwards, they merited to clarify their character until they drew near to Mount Sinai. After all the attainments, one must still submit himself and believe in God, because the ultimate attainment is recognizing His glory. This meal-offering that comes after the count is called a new meal-offering, as it has the power of rejuvenation since it comes from the knowledge in man…
This is the order in the verse: "And you shall count… and you shall present" – that is to say, that all of man's desire should be to clarify his character and attain knowledge, so that thereby he will know how to submit himself before Him. These two submissions are all of a person's service… And on Shavuot, which is the fiftieth gate, these two loaves unite.
