Recently I picked up "Prayer" by O. Hallesby at a thrift store. After some internet research, I discovered he was a professor in Norway at the Free Faculty of Theology in Oslo, teaching Systematic Theology.
In his lifetime, he wrote 67 books, but it was his radio speech in 1953 that brought him into the public view. As recorded in Time, he broadcast to Scandinavians.
"If you are not a believer, be careful! If you were to collapse and die suddenly, you would crash straight into Hell!"