First, we'll cover the chorus: The "we" in here is the Varden. It is the opener for an epic battle. Next we'll cover this stanza: Most of this song is about the final battle under Farthen Dur. The "we" in this part is Eragon and Saphira. The "valley" mentioned here is the huge valley of the Beor Mountains. Adding to the above theory about Eragon: I believe that the song is about Inheritance. The Eldunari being almost literally hearts of dragons