The Author's Musical Opinions

So, when Veronica Roth says this is a good song for Chapters 38 and 39 (when Tris is trying to get Four snapped out of the simulation he's trapped in by the Erudite) SHE MEANS IT.  The refrain for this song

"Hold on to the world we all remember fighting for
There's still strength left in us yet
Hold on to the world we all remember dying for
There's still hope left in it yet"

Is something that sounds like what Tris would be nigh screaming at Four, what her view of their world is, dystopian it may be.  She wants to fight for what she cares for, and at this point, she cares about Four.  She wants to save him from Jeanine, from himself.  She's desperate, not for her own safety, but for his own.  She sacrifices her own safety in a last-ditch effort to help him "Arise and be\All that [he] dreamed".