As we mentioned last time, at the end of the day, the arguments for the existence of God do not require supernatural revelation. They simply require the sense God gave a goose.
The problem however, is that we are not always able to have even that much sense. In the words of Pope Pius XII:
The human reason is, strictly speaking, truly capable by its own natural power and light of attaining to a true and certain knowledge of the one personal God, who watches over and controls the world by his providence, and of the natural law written on our hearts by the Creator; yet there are many obstacles which prevent reason from the effective and fruitful use of this inborn faculty. For the truths that concern the relations between God and man wholly transcend the visible order of things, and, if they are translated into human action and influence it, they call for self-surrender and abnegation. The human mind, in its turn, is hampered in the attaining of such truths, not only by the impact of the senses and the imagination, but also by disordered appetites which are the consequences of original sin. So it happens that men in such matters easily persuade themselves that what they would not like to be true is false or at least doubtful.
Thus, in the discovery of our capacity for evil, we necessarily discover the flaw in the "instrument" through which we are looking at God: namely, the cracked and dirty lens of our own fallen human existence. There is something wrong with us, which is why we snort and complain about humans being "dirtbags" (and why we ourselves hang back reluctantly at the ominous words "self-surrender" and "abnegation"). We can see some things about God through this dim and damaged reflection of him in our natural humanness, just as we can see some things reflected in a broken mirror. But there are other things about God which our own brokenness makes very confusing and hard to sort out (not to mention distasteful). Moreover, our status as creatures puts us in a very difficult situation if we wish to meet the Creator.
Here's why: Suppose Hamlet is looking around at his world. He would, as we have done, discover much to indicate that there was some sort of Mind behind his world—some Shakespeare out there—but there would also be a great deal to confuse and baffle him about the nature and purposes of that Mind. If he wanted to, he could, as we have done, try to get to know that Mind better by puzzling about the order of the world it has created. He could, as we have done, wonder about why there is evil in that world, why certain things happen there. He could, as we have done, guess from the fact that he is able to speak in beautiful poetry that the Mind that made him must have something of Beauty about it as well. He could, as we have done, discern even from the fact of evil in his world that there is a demand on him and everybody to be good and just. But there is one thing Hamlet could never do. He could never break out of his world and get into Shakespeare's world. If Hamlet is to talk to Shakespeare, Shakespeare will have to initiate the conversation.
Now we are to God as Hamlet is to Shakespeare. We are his creatures. We can make some good guesses about him based on what we see. We can infer that he exists. We can infer he is more like a Mind than the a mere Force. We can infer that he is an amazing artist. We can infer that he is personal. We can infer that he wants us to do the right thing. But we could also, like Hamlet, get a lot wrong, and waste a lot of time, and even commit any number of grave evils, since we also suffer with having our world and ourselves as distorted by sin as Hamlet's is. The mirror that should reflect Shakespeare clearly is broken and Hamlet cannot understand him all that well based simply on reason and looking at stuff around him. Moreover, Hamlet cannot, under any power of his own, leave his world to enter Shakespeare's. So if Hamlet is to know a lot more detail about Shakespeare—much less meet him—it is up to Shakespeare to make the first move and tell Hamlet about himself.
Scripture is the story of how God began to do just that in our world. It is the story of how God made a good world, how that world rebelled against him, and how he set about winning back a fallen humanity to participate in his divine nature after we threw it all away. This takes us to the next way in which God reveals himself: through the Sacred Tradition, both written and unwritten, of his people.
That's what Advent is about: the remembrance of God's revelation of himself to Israel (in the Old Testament) which culminates in the birth of Jesus Christ, who comes for one purpose--his passion, death, and resurrection so that we may be made partakers in his divine nature just as he, in the Incarnation, became a partaker in our human nature.