I agree - we sang this song in high school and I still have the sheet music (music and lyrics by John Phillips and Michelle Gilliam) which we used - it clearly says "You know the preacher likes the cold - he knows I'm going to stay."
I sat in the first row of one of the New Mamas and Papas concerts back in 1982 and that's exactly the lyric that Denny sang. John even told the audience the history of the song since it was written here in NYC.
The song was written in the early winter of 1963 and in every book or interview both John and Michelle state the inspiration for the song was how they spent a very cold day in Manhattan which was Michelle's first exposure to snow. Michelle didn't have any winter clothes and they were so cold they stopped into St. Patrick's Cathedral to get warm. And that's another reason that "the preacher lights the coals" lyric would make no sense at all. I've been to St. Patrick's Cathedral and its one of the biggest churches in New York City and has a very modern heating system so the preacher wasn't lighting any coals there, lol!
Rob