A black abyss, where no possible knowledge dare enter, predominates over the human mind. This destroyer of knowledge knocks all knowers off their foundations of knowing and back into the inane uncertainty which characterizes existence. If they are unprepared for a glimpse into this nothingness, then their tower of knowledge will collapse inwardly into nothingness.
We never experience this black abyss directly, on average, however; for most individuals never encumber themselves with metaphysical reflection. Nay, most of us are perfectly content with never picking up any single book on metaphysics, as we see no reason to engage in the subject matter. I think such an attitude, I must add, is also quite fine. The average person need not reason about their metaphysics, for reasoning about metaphysics shall lead to precisely the same outcome as never reasoning about metaphysics. So, there is very little practical use for this journey into metaphysics for the average person, especially if they already reject the notion of God on other grounds.
The average person presumes that with their regular sense-perception they can know what the world is like. We can glimpse onto the contents of perception and see a great many things, like: causation between two distinct events, interactions between numerous sets of objects, and the laws of the universe and their adherence to order. We learn of the world around us by directly observing it through the senses. Indeed, everyone seemingly adopts an empirical attitude towards the world: we make predictions about the nature of our toasters through sense-experience, we make predictions about the nature of our health through sense-experience, and we likewise make predictions about the nature of our friends through sense-experience; we presuppose the validity of our sense-perceptions without consciously doing so.
But when we do decide to encumber ourselves with the futile journey into the abyss, to take on that insurmountable challenge of seeing in the dark, we can no longer presuppose the validity of sense-experience. We must now bring into the fruition of consciousness the absurdity of presupposing the validity of our knowledge, only to conclude with the presupposition of our knowledge nonetheless.
When we rely on sense-experience for knowledge, the question can arise; why should we presuppose the validity of our sense-experience? Why is it that I assume the derivation of knowledge from sense-experience to be valid? Do I know that my senses do not deceive me? Do I know that, of the knowledge derived from sense-experience, it possesses truth? It is these questions which unravel all our knowledge, for the only way to justify our knowledge is through circular reasoning. In order to argue for the validity of sense-experience I must appeal to sense-experience; which is paramount to saying: A is true because A is true. Thus, because we cannot justify our sense-experience without appealing to sense-experience, we lack justification for the knowledge derived from sense-experience.
Because we are the subjects which exist at the receiving end of sensory input, we cannot know anything about the content beyond our sense-experience; therefore, we have not any grasp on what precisely resides beyond our sense organs, or if our sense organs deceive us. These states of affairs allow for the Christians, or any religious doctrine, to then suppose that it is God who grants us objective knowledge. That God, through divine revelations like the biblical text, has affirmed our existence and has given us objective knowledge. Hurray! We can go back to the grounds of knowledge and sanity, we are free from the metaphysical imprisonment of our sense-organs.
If only such were the case. Unfortunately, the religious rely as much on their sensory-experience as any other. They cannot possess knowledge beyond their own sense-experience, and so rely on their sense organs to justify their beliefs, much like the rest of us. They need to experience their revelations to discuss them; they must see, touch, hear, or smell their evidence of God. The readers of biblical text rely entirely on their sense of vision, the listeners of popes and priests rely entirely on their sense of hearing, and the consumers of Christ’s body rely entirely on their sense of feeling. The religious not only presuppose such things as being evidence of God, but they also presuppose the validity of their sense-experience as well.
So neither the empiricist nor the religious have justification for their knowledge, and so we cannot justly claim to know anything (including that very claim its self). Crashing down comes all our knowledge, into the abyss of futility it goes. We are doomed to know nothing and be forever locked into uncertainty. We must reject God and we must reject our sense-experience.