Why torture Moses?

Exodus 17:9 says, “And Moses said unto Joshua, Choose us out men, and go out, fight with Amalek: to morrow I will stand on the top of the hill with the rod of God in mine hand.

17:10 So Joshua did as Moses had said to him, and fought with Amalek: and Moses, Aaron, and Hur went up to the top of the hill.

17:11 And it came to pass, when Moses held up his hand, that Israel prevailed: and when he let down his hand, Amalek prevailed.

17:12 But Moses hands were heavy; and they took a stone, and put it under him, and he sat thereon; and Aaron and Hur stayed up his hands, the one on the one side, and the other on the other side; and his hands were steady until the going down of the sun.”  Why did Moses have to hold up the rod?  God killed the Egyptians while clearing his nose.  This is just torture.  Luckily, Moses figured out how to cheat the system.