In plain words
Rippling water breaks the one sun into many apparent lights; still water reflects it as one. So the Self seems many in an unsettled mind, yet remains one and untroubled. I am that ever-established Self.
Word for word
The one sun appears as many in moving water and as one in water that is still. Although He appears as many in the moving mind, He is one and without agitation. I am that ever-established Self.