That is itself, in a sense, our natural lot. Nature determines the good for us and obliges us to pursue it. But she has put us in circumstances that make its fulfillment far from easy. We share the world with bacteria, viruses, and wild animals, with earthquakes and floods, and with other human beings who share our limitations. What we need for our fulfillment is there for the getting, but actually to get it takes fortitude, hard work, hard thinking, and being in the right place at the right time. Being a human being can sometimes seem like being a humble sperm cell – billions upon billions with the same end, and only a tiny fraction ever realizing it. Or it would seem that way if we did not also by nature have immortal souls. The light of reason tells us that there is a God, that He is good, and that the sufferings of this life are not the end of the story for us. Thus does nature give some consolation even in the face of the obstacle course she has set before us. But only some – in part because she gives us no details about the life to come, and in part because even what she does tell us she tells us only under the best of cultural circumstances. Understanding natural theology requires some leisure and philosophical wherewithal. It also helps to live in an age which isn’t as intellectually decadent as ours is.
Original sin involves, in part, the loss of the supernatural assistance that would have removed the various difficulties of our natural state. Nature as God made her was good, if austere in the ways described. Nothing beyond what she gave us was “owed” to us. But God would have given us more anyway, by His grace – would have added to what had already been given us by nature, so as to enable us to get around her obstacles – if not for the Fall. The restoration of this supernatural gift is part of the meaning of the Incarnation, and thus part of the meaning of Christmas. But there is more to it than the restoration itself. As Aquinas says, the Incarnation was not in the strictest sense necessary for remedying the Fall, since God by His infinite power could have accomplished this another way. But it was necessary in a weaker sense, insofar as there was no more fitting way for it to be accomplished. (ST III.1.2) Quoting Augustine, Aquinas gives as one of several reasons it was most fitting the consideration that "Nothing was so necessary for raising our hope as to show us how deeply God loved us. And what could afford us a stronger proof of this than that the Son of God should become a partner with us of human nature?"
The problem of evil poses no intellectual difficulty for classical theism, in part because we have no reason whatsoever to believe that God cannot draw an outweighing good out of even the worst evils we suffer, and every reason to believe that He can and will. But it is an enormous practical difficulty, one that Christian theology remedies in a way mere philosophy cannot. Reason tells us to trust in God, but reason is cold, and falters in the face of a dying child. Yes, we are rational animals. But we are rational animals – creatures of flesh and feeling as well as of thought. And it is simply difficult to be a rational animal, a human being – to bleed, to feel one’s heart break, to suffer. The Son of God in His divine nature is beyond all that. Yet He took on human nature anyway, so that we poor men and women would not suffer alone. In Jesus Christ the God of the philosophers wears a human face. And in the end, “He will wipe away every tear from their eyes” (Rev 21:4). But not before crying some of them Himself, on a cross, and in a manger.