Reason is a useful tool, but we in Reformed circles tend to idealize or even idolize it (this coming from one who aced his Logic term while forgetting what Alexander the Great did). Reason is not our saviour, and the reality is that we cannot, however we may try, even use reason to demonstrate the existence of God. Moreover, it does not appear to be something that we should attempt to do--if God wanted it to be done, He would have made it possible.
Allow me to quickly (logically) prove what I just asserted. If you agree already, feel free to skip this next paragraph.
In logic, it is a fallacy (circular reasoning) to assume what you are attempting to prove, and to use it in the argument. For example: Scripture is infallible, because Scripture says that it is. Likewise, we cannot logically prove the validity of logic. We cannot give reasons for believing in reason, and if we illogically prove logic, then we have just falsified it.
Why is this? Why did God make the world in such a fashion that every belief must rest firmly on air? If we are questioned enough as to why we believe anything, we will end up in a corner where we can only say "Cause I want to." Every belief rests upon a foundation of assumptions: The Triune God of Scripture lives (Why? Cause He says so). The world reflects His Nature (Why? Cause He says so). He is a logical God (Why? Shut up and quit whining), therefore, logic is valid (to an extent--apply it to the Trinity or dual Nature of Christ, or even the death of immortality, and everything goes boom--you have a zero in the denominator, and "i" doesn't exist).
Well, if it is this way, and it is, it must be because God wants it to be this way. But why?
Because He hates formulaic, stainless steel, small minded people who stare studiously at the ground as they trod on towards sanctification. Look at His response to Job: He made bugs. Where is the logic in a centipede that hangs upside-down on cave roofs and eats bats? How is that rational? There are butterflies that, as grubs, emit a chemical making them smell identical to ant larvae. They are then collected and raised by the ants. However, there is a wasp that has the ability to tell the difference between ant and caterpillar larvae (though the ants can't), and lays its eggs inside the caterpillar larvae by invading the anthill and releasing a pheromone that causes the ants to attack each other, instead of the wasp. The wasp's young are then studiously raised by their mortal enemy, the ants, until they hatch, and the entire process repeats.
How, in any contortion of the mind, is this formulaic? How is this neat and clean? This makes no sense at all. Look at the duck-billed platypus, at narwhals, and learn the nature of our God--it is logically absurd. Where is the efficiency, the cleanliness? How many cockroach young are laid, and how many survive (thank God that the ratio is that low; why does the cockroach even exist?)? We serve a God, Who--without being disrespectful at all--wears white socks and Dockers with His tux. He makes no sense to our little reformed logical minds, which we all too often forget. We somehow manage to--God forgive us--grow bored with His predictability, as He is meticulously planting flowers (of an astonishing complexity and a staggering beauty), and then happily making bugs eat them before they bloom. Then something else eats the bugs. And He does this on purpose. He creates one of the most brilliant composers the world has ever seen, and makes him go deaf. He creates one of the most patently evil, demonic dictators that the world has ever seen, then, laughing like an irreverent schoolboy, pencils in that mustache that simply cannot be taken seriously.
So forget logic. Go lie on your lawn and watch bugs. Let a cow suck on your fingers, and explore the nature of this world. Logic does have some small part in our lives, but it is not the part that we give it. Let us delight in the absurdity of God--let us appreciate Him for Who He Is, not who we would have Him be. "He is not, after all, a tame lion."