This weakness is observable, and admittable by even the metaphysically blind. Even with our flaws in perception we can clearly see that humans are not flawless in their perception. Just as a dog cannot play the clarinet, so humans do not perceive clearly, accurately, or consistently. Our weakness actually goes much deeper than just an innate intellectual or conceptual disability--it is a spiritual and moral chasm. We not only do not have the mind or eyes to see the truth, we don't have the heart.
The existence of our perceptual fault of heart and mind lead me to an inescapable conclusion: we will never be able to intellectually find our way to God, nor for that matter establish that there is no God to find. We have the existence of stuff and ourselves and a puzzle that our intellects cannot reliably solve. Forensics and even a Commentary from the Authority (the Bible, in case that wasn't clear) will fail to objectively produce unequivocal, normative knowledge of God among humans, because its ascertainment is still dependent upon our perceptive abilities which are hampered by perceptual disabilities.
So what does it actually take for us to know anything about God? It takes imputed knowledge that gets past the limits of our perception, and arises intact from the inside out. It's not that forensics, or that revealed in the Commentary are not helpful, even essential, but they do not produce objective, reliable knowledge on their own. Logic, science, even the Word of God, are the prisoners of our perception. If the Holy Spirit doesn't anoint our eyes, ears and heart, we don't get the truth or we color what we do.
Nature is not enough, logic is not enough, even the Bible is not enough--it takes the Spirit to know God.