"I'll Take You There," by the Staple Singers
Singing isn't my new religion, but I love it infinitely more than I ever did that old religion (I find it infinitely more useful, too). And I think I get the use of "soul" when it comes to singing (and playing): it's artful and sincere, it makes you and the singer(s) and player(s) ecstatic or sorrowful (mostly the former, in my experience).
Heck, I'm just running my mouth. Listen to this song, its soulful lyrics, its soulful players, its soulful singers, the soulful woman singing lead. You'll know what I mean.
(Of course, the joke's on me because I think they're all talking about heaven, and I don't believe in heaven.)