Windows

It seems as though Angel is comforting someone who's fighting demons of some sort.

In this song, windows are a metaphoric way of being open and free to the world-- seeing the sun, feeling the wind in your hair--being alive. "Windows" can also be taken literally if the person she is comforting is too depressed to even get out of bed...

She is telling this person that it's okay to feel this way sometimes, because it's normal for everyone to have a past come back and haunt them from time to time, (as stated here):

"we throw our shadows down we must throw our shadows down we live and throw our shadows down it's how we get around in the sun in the sun"

And it's true; you cannot dwell on things in your past, (or even on things that hurt you in general). You cannot just sit around and let life pass you by. Yes, there will be shadows following you when you're out in the sun, but outside, there is beauty in the world: there is wind in your hair-- there is light.

She's asking someone to open their heart. The windows are the heart, the light is love.

I've often thought this song is the singer/narrator speaking to herself. Questioning her own fear, depression, or hesitation to engage with the world. And it's really sad because she can see the way out (the window and the light), but this inner conversation between the "light" and "dark" parts of the mind is neverending. The window might never be opened.