A thread with no answers referencing a dead website. Dead website also has no answers but speculation. One person posted "mediafire. com/?xfj7p38y97z8dey - 04 Fly.mp3" which is likely either the same track, the actual Jars of Clay song, or possibly a virus. I couldn't get the link to work.
(Not linking to it, but) a music piracy website which has the track listed under Jars of Clay, but no copy of it available.
What a mystery. The only idea I have is that someone figured they could "publish" their song by putting it on piracy websites under Jars of Clay's name, but the background vocals make me doubt that. I'm not sure someone would have the resources to do that but not to publish.
Yeah, that first forum post was also by me. My best guess is it was a track that got recorded but never released, then found and falsely attributed to Jars. Might remain a mystery forever, though.