verbiage and linkin park

tara and i listened to linkin park’s newest single “what i’ve done” and she pointed out a possible word error.  our main point of interest is the chorus:

so let mercy come
and wash away
what i’ve done

i’ll start again
and whatever pain may come
today this ends
i’m forgiving what i’ve done

is “mercy” the proper word choice for what the narrator is trying to convey?  tara argued that mercy is not receiving punishment that is deserved.  on the other hand, grace is receiving what is not deserved.  of course, mercy fits better with the meter, but it seems that “grace” is actually what the singer wants to come.  i should call him and ask.