Hiya,Marley!

Welcome to the "Gord Board". Looks like you'll be last (but not least) to join us this year. On behalf of Florian and Charlene (the board moderators) we hope you'll "set a spell" here for awhile. I'm just Borderstone,"the guy with the
most posts" (messages).
Anyhow,in answer to your Question,I read the lyrics here on the site and it simply seems to not just be about Gordon's shadow knocking on the door of this woman he loves but also about shadows of the past or the shadows we see in the day or the night. All of which are uniquley combined in this very romantic song.
Simply said,it's about a love you can't forget and sometimes revisit (like folks who break up & reunite.) Or,revisit in your mind.

Hope that's a good answer,that's just how I read it. Catch-ya later!