Ok just went thru that part 30 seconds ago and
That lever is used to open a secret room further on after you kill Amon I think his name was. It is used in the room after that little bridge area you go under where you kill him.
The room that needs the lever is where you pick up that key half buried in the broken vases to open the cage door.
Not much in the room for me though, little bit of cash and a spinel gem.
