Are you just talking about knowing Jesus Christ, which sort of sounds like they already believe in God and maybe being reborn? Or are you talking about a person believing God doesn't exist, or being the ultimate non-decider and choosing to be agnostic?
It would be good to know that you can be agnostic and still make it to heaven once your uncertainty is resolved. Because quite honestly, it seems that God has gotten a lot of negative publicity as far as the rage and anger departments go, as well as the 'you-better-believe-in-me-while-you're-alive-or-you're-going-straight-to-hell-when-you-die' department.
Regarding being agnostic, I always wondered, assuming God exists, how He could condemn a person to hell, if that person used their God given brain and determined they just couldn't know if God existed or not. It seems to me, people like that could really use a personal experience to convince them of God's existence. What does a person have to do to get such an experience?
Sadly, I have a sinking feeling what you mentioned is a view held by just one, or a small number of religions. I'm pretty sure they don't all say this. And if God exists, I'm pretty sure He doesn't favor one religion the most. Although, He may disfavor some. But that's just my $0.02 worth.