Is it Guardians in general? The Traveler coming brought the Darkness that killed us, only for him to send Ghosts to bring us back to life. We are now the Traveler's army, no longer having any other intentions but to save it. Yet, while we are still fighting for it, we only learn so much about our enemies and the Traveler itself that we beg to question what was life without it? We've only read books about the Golden Age, but can't remember experiencing it, despite living through it? Just a random guess. I'm decent at riddles, and this is a good one if I do say.