It isn't about what we believe, it is about what is True and what He says is True and how we respond to Him and His Truth. Lots of people believe lots of things, many of the wrong, (some of them get it mostly right) because they are led astray by what appears to be God's way, but it is not. The choice is what we want to believe vs what God says is True. We are supposed to take every thought and put it under the authority of Jesus Christ. ouch!
How would you show what is true, without believing?