I think this song is basically explaining the end of the book and the movie 'The Mortal Instruments. at the end of the movie, he calls her a mundane. when she realizes she isn't a mundane, she goes after Jace. Jace tells Clary to take her time, he'll wait for her, implying something more. "I'll be here waiting, hoping praying, that, this light will guide you home, for when the darkness comes." so when they both feels lost about their feelings, they hope each others love will guide them back to each other.
I think this song is basically explaining the end of the book and the movie 'The Mortal Instruments. at the end of the movie, he calls her a mundane. when she realizes she isn't a mundane, she goes after Jace. Jace tells Clary to take her time, he'll wait for her, implying something more. "I'll be here waiting, hoping praying, that, this light will guide you home, for when the darkness comes." so when they both feels lost about their feelings, they hope each others love will guide them back to each other.