Rabbi Shimon Felix
Broadly speaking, leaven is seen as a symbol of surfeit, appetite, gluttony, and desire. The matzah on the other hand, is seen as not only the bread we ate because we were in a hurry to escape affliction, but also the bread of affliction itself, the bread of the destitute, which we ate as slaves in Egypt.
In this nexus of symbols, eating the matzah is a way of identifying with the poor, oppressed and downtrodden, and of rejecting the excess and luxury of the oppressor — imperial Egypt with all of its decadence and excess. A sinful, oppressive, inhuman Egypt, which enslaves and murders strangers in order to build itself magnificent monuments, is what we reject by shunning the richer leavened bread and eating simple matzah on Passover.
With this in mind, we can see the insistence on only serving matzah in the Temple, all year round, as an attempt to make the Passover revolution against imperial Egypt an ongoing one. By prohibiting the baking and eating of leaven in the Temple, the Torah is turning the revolution of Passover, in which the oppressors were punished and the oppressed were freed, into an ongoing, permanent value in Jewish life.
Just as, when we sit around the Passover Seder table, celebrating, we are commanded to eat the bread of affliction and thereby, even as we celebrate our own freedom and autonomy, identify with the downtrodden and enslaved, so too, in our Temple, which represents national strength, autonomy and independence, we are forced to reject the hametz of the rich and oppressive, and eat matzah, the bread of the oppressed and the poor. This acts as an antidote, a corrective, to the kinds of feelings which could easily be engendered around the Passover table or in the Temple; feelings of self-satisfaction and self-congratulation, of power and possession, which we must reject, or at least temper.
By eating matzah and refraining from hametz, we embrace, both at the Pesach Seder that celebrates our birth as a nation, and in the Temple, our national religious center, solidarity with the oppressed, the poor, and the enslaved. This is the symbolism of the mincha, the kosher for Passover grain offering offered daily in the Temple.