I interpret it as just the hand that erases can re write what is gone... in other words just the one who does a thing, can say why it was done.

But there are other interpretations like:

the hand, representing the human individually, that "erases" or moves away from preconceived constructions can "write" construct, build, or create the true thing. In other hands, to be able to know the truth, you need to move away form what exists and go beyond that.