With all the charlatans who have preached in my lifetime, I am not going to listen to someone who says I have to believe the witness of certain people or spend eternity in hell. There are too many competing religions making the same demand for contradictory versions of history. You may find this kind of theological bullying to be comforting, but I don't. If it comes to that, count me among the weeds.
Don't you find it even a bit ironic that with all the horrible forms of pain that people can inflict on each other, the only unforgivable sin is our own private thoughts? Sorry, but I don't believe that is true, and I am unlikely to take anyone's word that God said it.
There is only One Person who has presented His Word for you to believe. Based on His credentials (resurrecting Himself from the dead) I would say you should give serious consideration to what He says.