to set fire to the rain i believe is like a comparison to her strongly over coming the sorrow. the rain represents being sad and to set fire to it, fire destroys, so she is causing a seemingly impossible distraction lol i am not totally sure though
i heared its about her being with a guy who turned out to be gay, so she is showing love towards a guy who wont take it the way she wants him to. fire to rain. they dont go togetehr.