1. By tradition we say that God the Father concerns himself with the entire universe; the Holy Spirit, with mankind, especially with its multiple kinds of unions through charity; and the Son, with the salvation and happiness of each individual.
But we can also look at it this way: the Son died the first time so that the world could be created; the second time at birth to unite humanity to the Godhead; and the third time on the cross to save individual men. But I’ve written on this extensively already.
2. The reason for man’s essential corruptibility and the inevitability of the Original Sin was the excess of potency in him. Angels are rational but have less potentiality in them and so are metaphysically safe; animals have plenty of potency but are innocent for being irrational.
As a result, man is a uniquely miserable creature. Blessed is the Lord for creating us anyway and providing an astonishing remedy for our inherent defects!
We can further see that the fall of the angels was a dispute between creatures and did not involve God. Lucifer was not so stupid as to rebel against the infinite and almighty God. His nature is and always has been intact. What happened rather was that the angels were given the grace of charity for men, as per the Holy Spirit’s mission to the world, but Lucifer despised humans for their (future) foibles and refused the grace. He then decided to wipe us off the face of the earth, not directly but by inclining us to murder each other. It should please us that the world, though it is beset by conflict, is after all not insane.
Note also that the demons will not be “punished,” as if they were part of our “civil society” of rational creatures and committed some crime. We are not cops who apprehended suspected criminals who will be granted all the requisite due process; if convicted in a court of law, “punishment” will be administered to some demons perhaps to deter others from harming men in the future. We are not a society disrupted by occasional sporadic disorderly conduct; we are at war which is total and merciless. The demons will be not punished by a civil authority but defeated in war and forced to surrender unconditionally.