I was going to say, about "Dark Was the Night, Cold Was the Ground," that it's a sound that's sort of stereotypical for the blues in a movie or TV way. I know, it's not a blues at all, either musically or thematically--it's religious. But sonically it's the kind of thing a movie or TV producer throws in to suggest blues, and/or the rural South or maybe West of the first half of the 20th century. And in that respect it's very misleading. I have a fairly wide, though not encyclopedic, acquaintance with the country blues--the acoustic blues recorded in the 1920s and '30s--and I don't know of another recording from that period that sounds anything like this.
In fact the blues is as likely as not to sound pretty upbeat, even when the lyrics are bleak, and the lyrics often contain a lot of humor. It wasn't played only on street corners and in the fields--it was party music as well.
Anyway, the same is true of gospel, which was mostly what Blind Willie Johnson played. Here are a couple of much more typical tracks.
I'm pretty sure he didn't write either of these, as they show up fairly often in the repertoire of other artists, including '60s folk revivalists. You can read about Blind Willie Johnson here. In case you don't want to bother with that, here's something fascinating that I learned from it:
"Dark Was the Night" was also included on the Voyager Golden Record, copies of which were mounted on both of the Voyager Project unmanned space probes. Carl Sagan, who was involved with the selection of the contents of the record, chose the song as he believed it properly encapsulated the essence of loneliness that mankind often faces.
The fact that Carl Sagan chose it is interesting, and a bit touching, really. But Blind Willie Johnson could have taught him something more. It's a good example of God hiding things from the learned and revealing them to the little ones, intellectually speaking.