Not so much the meaning, but the marvelous orchestration. It builds steadily to a resounding climax, then eases through a calming afterglow into silence. As for the lyrics, I think it is a song expressing a traveler's loneliness on the road, loneliness for the one he loves and has had to leave behind. To ease his pain he has resorted to some mind altering substance to ease the pain. But he still longs for her. It's more about the mood the music set than the lyrics.