The Midrash comments that Hashem created Yam Suf on condition that it would split when called upon to do so by the Jewish people. Why was this condition necessary? G-d controls nature and could easily have forced the Yam to split even if this behavior was not built into its nature from creation.
G-d created the world with both a moral order and a natural order. I heard in the name of R' Chait (of Yeshiva Bnei Torah in Far Rockaway) that yesh lachkor whether these are two seperate "agendas" (if you will) or not, i.e. does the natural order function in harmony and concert with Hashem's plan for moral order in the world, or is moral order imposed on creation from without, and nature is at best a passive canvas? It seems to me (I did not hear this point b'shem R' Chait) that this Midrash speaks directly to this point. The splitting of the sea did not place the moral order in conflict with the natural order of the sea and force one to bend before the other, but rather nature was created with moral order woven into its fabric so that these forces never come in conflict.
With this in mind we can better understand the strange reaction of Hashem to Moshe's tefilos. Moshe faced the sea before him and the Egyptians in hot pursuit and so he began to daven. Hashem ordered Moshe, “Mah titzak alei, debeir el Bnei Yisrael v’yisau”, to cease tefilah. Why? Isn't tefilah our instinctive and appropriate response to danger? The answer is that tefilah by its very definition is a cry that emerges from our perception of a disconnect, a chasm that lies between what we see in the natural world and our expectations and dreams based on the moral order of things. We ask Hashem to interfere and dispel sickness, death, tragedy, all the calamties of the natural world, in response to moral zechuyos. The splitting of Yam Suf as per the condition of its creation was a purposeful statement that despite our faulty perception, there is no real disconnect between the moral world and the natural world (see the Shiurei Da'as of R' Bloch on Shirah and see my article "Split the Difference" on the Kallah Magazine website for more on this idea.)