Humans lack the ability to access truth directly. More often they acquire truth indirectly.
In terms of truth, there are roughly two camps of humans, one with extrememly small amount while the other the mass majority.
When you trust your own five senses, you joined the first camp of humans deemed as the eyewitnesses. When you are unable (as limited by human inability) to contact truth directly. You joined the second camp of humans deemed as the believers.
Even science works so. Do you know that black holes exist? You do. Do you have the evidence? You don't. Information (truth) functions as a piece of human testimony from eyewitnesses which we call them the scientists. There could less than 100 such scientists dedicated and specialized in researching black holes, versus the 8 billion humans on earth. That is to say, the 8 billioin humans need to put faith in the 100 scientists to indirectly get to such a piece of truth. That's how reality works.
Now how do we know the the truth of black hole with its characteristics are truly from scientists other than swallowing with faith? Subconsciously we rely on evaluating the legitimacy of what this piece of testimony is conveyed. From the authorities behind the testimony who authenticate the information, and from the consistency of how information are conveyed (if I said the in center of a black hole, there's a large stone, you shall not believe because this is inconsistent with information (a testimony) flowing). We get to the truth of black holes from journals we deemed reliable, TV channels we deemed reliable, education entities we deemed reliable. Subsequently these entities we deemed reliable are authenticated by the central government. One of the government's duty is to remove untrustworthy media conveying falsehoods. You may need to overthrow it if you don't think that it enforces the conveying of truth.
As for the Bible, the intangible media conveying its information are the physicla churches (you might choose to read the Bible by yourself though, yet in terms of a media in a larger scale of conveying information the churches are the role). The situation is governed by an intangible Church which utimately refers to the Temple built by Jesus in three days. It is somehow linked to God Himself (Jesus is the head of legitimate churches), in terms of authority and authentication.
Other than this "business as usual" flow of conveying truth, God the Holy Spirit is also poured upon Christians to guide them through. However, this is tied to basically two factors, which are 1) where your faith is, and 2) your distance from the sin-incompatible God.
As Jesus put, you can move mountains if you have enough faith, while He also put that His direct disciples' faith is smaller than the smallest seeds in the world. So you still need the authenticated Church to maintain a standard (though intangible as well).
Distance to the sin-incompatible God matters as well. How close you are to God? In 60s there could be less than 1% Christians can actually get in touch with pornography, but today the opposite may be true that less than 1% Christian haven't get in touch with it. To a certain extent, this measures distance from God of today's humans. Again, I don't think that you can rely on this factor alone without the intangible standard from the intangible Church. No worries yet, the final statement is that if you are His sheep you will hear His voice. Those endure to the end by doing the will of the Father shall be saved at the end. Not a single sheep will be left behind! That's the promise.