Lyric discussion by mezzoforte 

Cover art for Burn lyrics by Ellie Goulding

My thought on this song is that fire = purpose or a cause you believe in strongly (such as gay marriage, equality for all, etc.) and burn = the spreading of the "fire"

This is a song about standing up for what you believe in and being with others share the same dream because there is strength in numbers and the more people that believe in the same cause the greater chance for acceptance or change.