Christians are under the forgiveness. Atheists are not. For sure, the atheists better take it literal and do it.
That depends on how you interpret the bible...
The church I went to believed... once saved, always saved... in that case, since I was "saved" at the ripe age of 4 years old... I'm still going to heaven
Once saved, always saved, is not Biblical. The writer to the Hebrews talks about people who fall away as never being able to be brought back. Thus, it is possible, although it is unlikely, to fall away.
I am not speaking about you, personally, here. For all you know, because you have the once saved always saved idea in your head, you might be a false atheist, and simply don't know it. There may be chance for you yet.
