"If I could I surely would stand on the rock where Moses stood" probably means I would free my people just as Moses freed his. I think the originator of the phrase visualized Moses as standing on a rock when he raised his staff and caused the waters to part. The next phrase "Pharo's army got drowned" is to reinforce the allusion.

This reminds me of a story:

Moses is standing at the shore of the Red Sea with his PR man.

"Abe," he says, "have you ever seen such incompetence? Here we are standing at the edge of the water, the Egyptian army is right behind us, and those idiots forget the boats! What do they expect me to do raise my staff and command the water to part?"

"Do that Moses, baby," says the PR man, "and I'll get you four pages in the old testament.

Murray