It's a play on the common phrase "there but for the grace of god go I", which means that were it not for god looking out for you your fate would be the same as someone less fortunate.
And as I watch the drops of rain
Weave their weary paths and die
I know that I am like the rain
There but for the grace of you go I
So in the context of the song he is saying that were it not for the love of the woman he is singing about he would as lost as a drop of rain. Hope that helps. Good song.
Bad grammar for:
I walk -in front / in the light of- -your grace / gracious firgure / graciousness.