When you get down to it, it seems the explanation is that God can't save us without Satan to tempt us to do evil. Which, of course, means that God is not really all-powerful and is, in a sense, dependent upon Satan. Christianity is fundamentally like Zoroastrianism and Manichaeism in that respect.
The JW explanation is that Satan called into question God's right to rule over his creation. We need to hang in there and keep worshipping him until he proves to the whole creation that he is right and we can't do without him. Our suffering, like Job's, is just collateral damage.
I almost tried to make sense of this. lol