The British adventurer, himself a Christian, was the first to circumnavigate the Earth through both the North and South Poles.
He did so with South African Charlie Burton - also a Christian. Oliver Burton accompanied the two for the Antarctic leg of the trip.
Mr Fiennes told Cheltenham Literature Festival that when selecting potential adventurers to go with them: "The ones that we fancied had all marked religion as a ten-pointer [out of ten].
"Sure enough, at every turn they proved good.
"I held church services in the tent every Sunday. Obviously you can't have hymn books because they weighed too much.
"The only thing that all three of us knew was one verse of Jerusalem."
But Ranulph Fiennes said even faith in God had its limits.
"When you're out there, your fillings fall out in the cold, you get gangrene, crotch rot.
"Although I have this faith it isn't strong enough to fight crotch rot."
