A person's sustenance is as hard as splitting the Reed Sea. And that Hashem accomplished with two letters. A person has to make as much of an effort as he can in order to sustain himself and those who depend on him. Although everything that we receive is decreed on Rosh Hashana, nevertheless, Hashem requires us to make an effort to help ourselves as much as possible. In this way the splitting of the sea and a person's livelihood can be equated.
Beginnings are always hard.
And it was hard for the Children of Israel to plunge into the Sea of Reeds, pursued by an army of Egyptians who wanted to drown them. All we have to do is try, and Hashem will make sure that neither the Egyptians, nor the bills, will drown us. It happened that when Moshe raised his hand Yisrael was stronger, and when he lowered his hand Amalek was stronger. That force is called Amalek. The Jewish People stand immutably in opposition to that idea.