We humans have no direct knowledge of God. For knowing a truth or a good is to know what is concrete, not abstract. All communities of knowers share language, information, questions about that data, hypotheses as to their meanings, judgments of validity, and responsibility for what they know. And while what is true or good is always what is true or good about this or that thing or event, knowers only know the real abstractly. This is to say that human knowledge is at best, conditioned, that is to say, virtual: there are always more questions raised by answers.
Beyond the limit that intelligence runs up against is the fact that we can only know this universe, what we theists call creation. When a person asks about the meaning not of something specific, but rather the “meaning of meaningfulness (and apparent meaninglessness)”, the “sense of the sacred” makes itself felt.
No matter whether that person believes that such feelings have no base in reality, this phenomenon is one that all people experience from time to time. It is at the base of idolatry as well as authentic faith. Idolatry seeks to control via ritual and ideology (imposed meaning) both why living seems to suggest both a deep meaningfulness, and, at the same time, a measure of absurdity.
Making idols, something we are all good at
Idolatry is the futile attempt to manipulate the universe as humans experience it, think about it, talk about it. It is the making of our own god(dess), whom having made it, we can name and control, and this in particular for those in power. We can ascribe all sorts of good and evil qualities or make up a pantheon of figures with those (and other) attributes. Thanks to the Hebrew Scriptures, the old physical idols are gone forever. No one seeks to worship a golden calf anymore. A religion such as Hinduism has indeed a pantheon, but those divinities are not thought to reside in their images, as the gods and goddesses of antiquity were believed to be.
Which brings us to Thomas Aquinas and his “quinque viæ” or “five ways” in his masterpiece, the Summa Theologicae or “Summary of Theology” (see I.question 2, article 3). It is his response to two very modern assertions: a good God cannot exist because there is evil in the world; and, since all things can be reduced either to nature or the reason and will of humans, there is no need of God. Thomas’ respondeo appeals first to motion, then to cause, thirdly to necessary prior existence of any existent. His fourth way is to the chain of being: “Now the maximum in any genus is the cause of all in that genus; as fire, which is the maximum heat, is the cause of all hot things. Therefore, there must also be something which is to all beings the cause of their being, goodness, and every other perfection…” And finally, Thomas brings in teleology — all things have an end toward which they are oriented — and therefore some intelligence external to them has to gift them with that purpose or end in their creation.
Of course, these Ways are not convincing, even if they continue today to point beyond themselves. Nor did Thomas imagine that they would convince anyone of the reality of the living God of the Scriptures. The Five reproduce “what everyone (in the 13th century) calls God” but what God actually is cannot be divorced from revelation.
God-talk is everywhere
But what the Five do is underline the point that every language has a word for “god”, and that the only way humans can approach that is through indirect means without revelation — and even with Scripture, it should be clear that in this respect we are no better off. No one can see God and live, not even Moses (Exodus 33:20); from this we understand that no one can know God a se, the divine whatness. We can ask why there is something and not nothing: what set the universe in motion, what caused it, what ordered it… But what is not of the reality we experience we cannot know. Our knowing is at best a correct abstraction from the concrete, the real as we encounter it. Our attempts to ask whether there is a God can therefore only be a reflection on abstraction itself.
The Gospels, however, do not make us claim to know. The great philosopher Ludwig Wittgenstein made a remark about the Gospels that is pertinent. “Christianity…offers us a narrative, and says: now believe!” 
 “Si Dieu nous a fait à son image, nous le lui avons bien rendu.” — Voltaire, Le sottisier. (If God made us in his image, we have certainly paid him back.)
 “But the hour is coming, and is now here, when the true worshipers will worship the Father in spirit and truth, for the Father seeks such as these to worship him. God is spirit, and those who worship him must worship in spirit and truth” (John 4:23–4).
 They are not really proofs of God’s existence, though he begins by saying, “The existence of God can be proved in five ways.”
 The great scientist Pierre-Simon Laplace in a (possibly apocryphal) conversation with Napoleon Bonaparte, told him that he “had no need of that (god) hypothesis” in writing his book on celestial mechanics — six centuries after Thomas wrote the Summa.
 Compare to Aristotle, Metaphysics, especially book 12.
 Jean Porter, Nature as Reason: A Thomistic Theory of the Natural Law (Grand Rapids: Eerdmans, 2005), 328.
 In Culture and Value, trans. Peter Winch (Oxford: Blackwell, 1980), p. 32.
[On the cognitional theory I reference, go here first and follow the linked stories. For a lot more, see my (so far) unpublished book, Set You Free: Know Your Own Mind. Write me for more information…]