Why did Allah create humans in such a way as to be liable to doubt? This is something that atheists ask in an aggressive way: If God is real, why did He make Himself hidden? If there is a God, why doesn’t He reveal Himself and remove all doubt?
And Allah addresses this charge directly in the Quran in multiple places. He says, If we sent down angels, if the dead spoke to them, if all kinds of miracles were shown to them, if literally every single sign was shown to them, they would still disbelieve.
One of the miraculous ayat in this regard is from Surat al-an`am, when Allah says: “If you are able to seek a tunnel into the earth or a stairway into the sky to bring them a sign, [then do so]. But if Allah had willed, He would have united them upon guidance. So never be of the ignorant.”
Allah is saying that even if you were to burrow deep into the earth or put a ladder up to the sky and bring the disbelievers and doubters a sign, that wouldn’t move their hearts one inch closer to belief.
What’s amazing about this verse is that, in modern times, this is exactly what has happened. We have drilled miles into the earth and we have gone miles up into the heavens and using telescopes we can see all these amazing, awe inspiring things in this universe, things that past people had never seen: galaxies, nebulae, pulsars, quasars, superclusters of galaxies. These are all ayat of Allah and they are so grand that they are literally beyond human conceptualization. We literally cannot fathom how large a galaxy is, how old the universe is, how powerful a black hole is and so forth. But we now see all these sublime things with our very own eyes, and none of that serves as evidence for the disbelievers.
Point being that even if disbelievers were suddenly presented with a whole other aspect of existence, no matter how unearthly, no matter how spectacular, they would always have a way to dismiss it or subsume it into their definition of “normal” and “unremarkable.” And Allah gives examples of past nations who did exactly this: miracles occurred before their very eyes, and they just said, oh this is just some kind of trick, this is not spectacular, this is just commonplace, this is not definitive proof that God exists, this is not definitive proof that God spoke through a messenger, etc. Because of their arrogance, they have become deaf, dumb, and blind.