These switches control which doors open and which doors are locked in the stairway of the Eastern Tower. If all handles are switched to the left, that means the switches are off (and thus all doors are locked). You only start with the middle switch in tact (you can find the other two levers in the doors you can unlock). Here I will go over which switch combination opens which doors and so on.

Switch #1 opens up Door #1.

Switch #2 opens up Door #2.

Switch #3 opens up Door #3.

If Switch #1 and Switch #2 are flipped,
they will open Door #4.

If Switch #1 and Switch #3 are flipped,
they will open Door #5.