More from R. Jonathan Sacks (link):
We have here two ways of seeing the same events: one natural, the other supernatural. The supernatural explanation - that the waters stood upright - is immensely powerful, and so it entered Jewish memory. But the natural explanation is no less compelling. The Egyptian strength proved to be their weakness. The weakness of the Israelites became their strength. On this reading, what was significant was less the supernatural than the moral dimension of what happened. G-d visits the sins on the sinners. He mocks those who mock Him. He showed the Egyptian army, which reveled in its might, that the weak were stronger than they - just as He later did with the pagan prophet Bilaam, who prided himself in his prophetic powers and was then shown that his donkey (who could see the angel Balaam could not see) was a better prophet than he was.
To put it another way: a miracle is not necessarily something that suspends natural law. It is, rather, an event for which there may be a natural explanation, but which - happening when, where and how it did - evokes wonder, such that even the most hardened sceptic senses that G-d has intervened in history. The weak are saved; those in danger, delivered. More significantly still is the moral message such an event conveys: that hubris is punished by nemesis; that the proud are humbled and the humble given pride; that there is justice in history, often hidden but sometimes gloriously revealed...
The genius of the biblical narrative of the crossing of the Reed Sea is that it does not resolve the issue one way or another. It gives us both perspectives. To some the miracle was the suspension of the laws of nature. To others, the fact that there was a naturalistic explanation did not make the event any less miraculous. That the Israelites should arrive at the sea precisely where the waters were unexpectedly shallow, that a strong east wind should blow when and how it did, and that the Egyptians' greatest military asset should have proved their undoing - all these things were wonders, and we have never forgotten them.