To quote Thomas Paine “God reveals himself in the creation we behold”.
In other words the complexity of the universe makes it evident there is an intelligent creator, we see no direct evidence that the creator intervenes in the affairs of man. Bible doesn’t count because it is only hearsay not direct evidence.
Perhaps the creator did write the rules in our heart as we see the in the empathy we naturally feel for those in pain.
If an account of a murder were written down by a certain recognizable person, and if such written account and the person writing it could be subject to test and triangulation, it could get a man sentence to death.
The Bible as a written account has been and is constantly being tested both in its facts and in its principles. It is proving to be a document of substance written by men of substance (and having no ulterior motive).
Obviously, we have to go with what we have instead of just assuming "nothing." Assuming nothing is like assuming the American Revolution didn't occur because no one alive or no video evidence can attest to it.
There are vast stretches of history (all of it in fact) that are based on nothing but written accounts. What kind of evidence do you want? Video?
As anyone knows, there are ways of testing and triangulating written and old accounts to get at the truth.
Without written accounts, we would have no account at all.
Perhaps you are correct in your beliefs...perhaps not.
But don't assume that because the path is difficult (i.e. circumstantial in this case) you can't find the Truth.
You can.
And many men have gone to their death (with smiles on their faces) believing in this Truth.;-)