For the source text click/tap here: Pesachim 27
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The Netziv turns our notion of chametz/matza on its head
What is the symbolism that leaven and unleaven represent in the Temple?
Leaven represents fulfillment, a process which has gone its due course. The ultimate and supreme form of flour and water is a leavened loaf.
Unleaven, on the other hand, is "not yet" what it aspires to be; it figuratively represents the beginning of a yet-unfulfilled process. It is presently immature and unripe. It is in the early stages of a journey.