A “knife” is that with which one slaughters. Devotion should be the reason that there will not be any flaw. For example, one who commits suicide is because of a flaw, since he has no point in living for several reasons, and therefore he commits himself to death. Hence, we must see that when one becomes devoted, it is not because of some flaw but because of the love of the Creator. This is why we check the knife, so there will not be any flaw in it.