I agree with that BB, but let me approach it from only a very slightly different angle. We know there are many spurious counterfeit cults and religions out there. These false religions and cults, are counterfeits to the truth. I think if there wasn't any spiritual truth out, Satan would not energize people to start false religions. The fact that false religions exist, should clue us in to the fact that the truth is out there too. And you are right. Knowing our Bible well, helps us see right through all the false religions out there.
Yes, there are MANY false religions and prophets in the world which proves that the TRUTH exists and is knowable. I remember learning that “there had to be truth before there was a lie”. Truth existed first - then the devil and all his allies came in and perverted it. I praise God that He gave us the “more sure word of prophecy” - His Sacred Scriptures - so that we can know what the truth is and His Holy Spirit to lead us into that truth.