This song became legendary, as a typical teenage love story that joins thousands of teen girls on this Earth, but I think that its meaning has gone lost and has been replaced with its incredible popularity in pop music industry.
It's the typical love song about unspoken feeling, so as many other Taylor Swift song. It's about the frustration of loving someone so much and not being able to let them know that if they only opened their eyes they would see true love is the one that you've always had by your side, no matter how far you try to go. Taylor - or should I say, the girl in the song, since this situation is more ficticious than autobiographical, as she said - sees the light shine through the boy she loves, knowing she's the only one who really knows and understands him, but somehow she cannot reach him, because he doesn't know how much she's willing to love him, or he doesn't want to see it.
If we want to consider the video, which can be taken as a little movie, we can also take its happy ever after as a hint to the fact that, in the end, true love finds a way. Anyway, the song is an explosion of feelings: frustration, desire, unfairness, resignation, and still hope.