I think the argument goes something like this: God created us "in His image"; he has free will, so do we. Satan suckered Adam and Eve into the Fall; God could surely coax us back into union with him by means of coercion, but if He had to, say, keep us in line by tossing lightning bolts at us every time we sinned, our obedience wouldn't be out of love, but out of fear. He took it upon Himself to reverse the Eden Calamity, and we, with our free will, can choose to accept or reject it.