The mind is given the power to hold or to release, and what it decides here it experiences as its whole reality. To bind is to fasten guilt upon a brother, and a mind that fastens it there fastens it upon itself, for it can only see in another what it first believes about its own worth. To loose is to let the other go free, and in that release the one who forgives discovers he is free as well.
So binding and loosing are never really done to someone else; they are choices about which teacher the mind will keep. What it condemns it carries; what it forgives it lays down. Heaven simply confirms the choice, because the mind's decision about its brother is its decision about itself.
Earth: the mind as it chooses in the dream, the place where forgiveness or condemnation is decided
Heaven: the reality that reflects back to the mind whatever it has chosen to hold or release