By retracing your steps through the Throne World, you've picked up enough clues to form a theory about Immaru's motives, if not his entire plan.
From the beginning, it was clear that the Throne World had—and still has—fierce protectors in the Lucent Brood. Their antagonism was an effective smokescreen for the fact that, behind the scenes, Savathûn actually wanted you there…
Unlike the Scorn. You recall Immaru's voice, after you swiped the resonant runes from his squads: "We got interlopers in the area…"
Interlopers. Not just Guardians, but any who trespass into the Throne World are the threat.
And the defense against them lies in the Dark-tinged Osmic Fragments and the runes imbued with Hive magic.
Just when you thought you had seen enough contradictions-in-terms in this investigation, up pops a Hive Ghost using tools of Darkness to protect a realm filled with Light.
In the meantime, there are other angles of the investigation to consider. Check the other Hidden reports for more leads.