I remember seeing this dramatic mini-series in the late '90s-'00s, but it may have been created in the '80s. I believe it was an adaptation from a book by a well-known author.
The setting was in the US after some rapture-like event. I don't remember the cause, I just remember that there were a very small number of people left, and almost all of them were critical characters. The portions I remember involved traveling through the desert towards a big city (Las Vegas?), and I believe the final conflict was there in the city. The main story was about this final conflict/showdown between these people who were representing the forces of good and evil. There were definitely some religious themes as well.
There are only two characters I remember. The main character was your generic conflicted Everyman with good morals, so not much detail there. The other was a gentle-giant type who was big and strong but had the mind of a child. I think he ended up being very important towards the end.
Unfortunately that's all I remember right now, but I'm hoping it was popular enough to be obvious to someone. The one series I know it's not is Left Behind. The one I saw was not nearly as directly Biblical.