Bob-- I am certain that the phrase has been used in several, if not many, songs, but I believe that the term goes back to the old Ptolemaic theory regarding the makeup of the universe, in which Heaven was divided into seven ethereal levels, or layers, and hell was similarly partitioned. I don't have time to check the details, but I believe that John Milton, in "Paradise Lost" makes reference to this highest heaven of all. Sorry that I can't be more specific, but I'm currently pressed for time.

Bill