He played the Star Trek fanfare before "Amazing Grace." It was too many notes to be a coincidence. I wonder if he comes from such a secular, non-Christian background that he thought "Amazing Grace" actually came from Star Trek.
Harve Bennett, who required Horner to include it in the music, had no idea what song it was when he heard it at a funeral. He just liked it as a melody and thought it should go in the movie. A lot of show business people don't know Christian music.