Chasidut su Esodo 15:15

Therefore leaven is permissible throughout the year, and only on Passover must we eat unleavened bread, while leaven is very strictly forbidden, even in the minutest amount. This is because on Passover, which represents the Exodus from Egypt, we must eat only unleavened bread, representing Providence, while leaven, which represents nature, we must completely eliminate so that it will not be seen or found in our homes. For the truth is that nature itself is also divine providence, but since pharaoh and the Egyptians greatly overpowered us and denied G-d by saying (Exodus 5:2) "who is G-d?", therefore it is impossible to take leave of Egypt other than by means of a very great revelation of providence. Therefore, during the Exodus, G-d revealed His providence with a very great revelation, performing for us awesome wonders. For this reason, we must eat on Passover only unleavened bread, which corresponds to Providence and not leaven, which corresponds to nature. On account of the intensity of the exile in Egypt, which comprised all the exiles, it is impossible to take leave of it other than by a revelation of Providence alone. Nature though, represented by leaven, must be completely eliminated, not to be seen or found. Nature would have empowered the Egyptians and then, due to their great power over the Israelites at the time, it would have been impossible to leave. For this reason, we must eat on Passover only unleavened bread, which corresponds to Providence and not leaven, which corresponds to nature. But since for seven days we eat unleavened bread, corresponding to Providence, we can then eat leaven throughout the year. Once we have already left Egypt and the knowledge of providence has been revealed by having eaten unleavened bread, we are then allowed to eat leaven, corresponding to nature. By means of the great revelation of providence we truly know that nature is itself providence, that G-d created everything and guides everything according to His will, and therefore we may eat leaven for the rest of the year. Only at the beginning, during the Exodus, it is completely for bidden to eat leaven, for at that time, due to their great power, it was forbidden to acknowledge nature at all, for that would have even further empowered them and we would not have been able to be redeemed. But after having left Egypt and Providence was revealed, we know that even leaven, representing nature, is also divine providence, and we are then allowed to eat leaven after Passover. This corresponds to what is stated in the holy Zohar, that once we received the matzo, the medicine, we may then eat leaven (Zohar II 183b). This means that after providence was revealed, we may eat leaven, for knowledge was increased and we know that even nature is really Providence. Therefore, leaven only became permissible after the splitting of the Red Sea on the seventh day of Passover, for that was the ultimate fall of Egypt. Providence was then revealed more than ever by the many miracles that took place then. Natural sciences, corresponding to the great power of the nations, were then subdued and eliminated, for they all were very terrified by the revelation of providence that took place, as written (Exodus 15:15) "then the princes of Edom were terrified". Thus the revelation of providence also revealed that nature itself is really providence and therefore, after the seventh day of Passover, it became permissible to eat leavened bread.