Both theists and atheists must face that scientifically the existence of God cannot be "proven" from one person to another (yes spiritually, but not scientifically). I often say that I am a scientific agnostic and a spiritual theist. That is so because anything that hypothetically exists beyond the universe cannot be proven using the properties of the universe. It is what we are bound by as well as what we are scientifically limited to when acquiring facts; however, there can be evidence. Having created the universe, the creator must exist outside the universe without being bound by its properties, otherwise he (illogically) created himself in the process of creating the universe. Figuratively, I often describe the universe as a massive sphere which includes all of its properties: natural laws, materials, organisms, atmosphere, and its sequence of events (i.e. time), yet God exists beyond its boundaries. Consequently, by existing outside of time where the laws of cause and effect do not apply, God does not need a cause, nor is he made up of such properties we use to detect "being".
Not only is it more probable (though probability is, on the contrary, not always the dominant factor for an absolute justification), but the physical undetectability of God is necessary. If he indeed showed himself in a more definitive manner, or according to our visual awareness (e.g. waving from the clouds on a golden sleigh, giant hands lifting mountains, etc.), a power so far beyond the universe suddenly interjecting the universe would demolish all in the vicinity [Richard Deem; God and Science]. This is justified by the very words of God, in Exodus 33:20, saying, "You cannot see my face, for no man can see me and live."
Simple examples tend to put seemingly great complexities into perspective. Imagine the power of a star resting billions of miles away. The light shines so brightly, it can still be seen regardless of its distance, but it is days old by the time it reaches our eyes. We know that human vision is harmed when staring into the closest star of all, the sun. The creator of substances as powerful as these must have a natural light far beyond any of the creation, including the power of the stars, therefore it is for our own good that we cannot see God in full form.While physical intensity is an important factor, if made dominant a physical presence of God over spiritual presence, would not all reasoning behind human creation be rather futile? John 4:24 says, "God is spirit, and those who worship him must worship in spirit and in truth." Because the utmost authority is a spiritual being, our limited, physical perception is a symbol of our existential deficiency without that authority. This is so because, ultimately, we are formed for the glorification of God rather than merely forcing him to task in order to satisfy the human nature of self-delusion; God extends beyond secular conventionalism.
But why call it "the human nature of self-delusion"? Our senses rely on our own cognition, which is not always a detector of absolute truth. Rhetorically speaking, of what purpose is glorification through creation if it has all been given with no realization of his spiritual superiority? Because God is holy, he does not sin nor does he drive us to sin, therefore, he cannot fuel such a disorderly universe. In order to gain an understanding of God, a man should first humble himself before God (Daniel 10:12), which is entirely different than living with a derisive expectation for signs or evidence. A common mistake we make is that we look for God in places where we ourselves wish to find him, yet even in the physical reality this is a complete failure. For example, if you lost your car keys, you would not search where you want to search, you would search where you must in order to find them.
There are some arguments, influenced by Greek philosopher Epicurus, that suggest God's "insensibility" to our physical perception is evidence for either an apathetic God or a malevolent God. The following is a quotation by Epicurus that is quite popular among many skeptics, "Is God willing to prevent evil, but not able? Then he is not omnipotent. Is he able, but not willing? Then he is malevolent. Is he both able and willing? Then whence cometh evil? Is he neither able nor willing? Then why call him God?" On the contrary, it more so signifies a God wanting closer, individual contact with the creation. According to the common analogy "man was created in the image of God" (Genesis 1:27), the validity of it is evident, in some cases, when one applies how a human would feel in a relationship as to how God would feel. We have better relationships with those who truly seek us rather than those sitting on the couch watching us move mountains trying to prove ourselves. It is fairly evident, however, by the biased human perspective, such as "make this cup of water float, then I will believe" or "give me a stack of money, then I will believe", we are often diverted from the supernatural perspective God has given us in order to comprehend his existence. This is why our very own common sense can be our worst of enemies, or as stated by Albert Einstein, "Common sense is the collection of prejudices acquired by age eighteen."