They're never going to tell us. All this speculation is just a pointless waste of time. You know that, right? So with that said, here's my theory: Imagine if you could send information back through time to yourself. You might use this power to avoid misfortune or exploit a game of chance. But you could also use it to gain new information you don't know even in the future by creating a causal loop. Say you want to open a combination lock. You tell your past self that the combination is 0000. When that doesn't work, your tell your past self to use 0001. In this way you guess until you get the correct combination. Any iteration in which you try an incorrect combination is erased from the timeline. In a more complicated form, this is the function of the Vault, and the reason the Oracles and the Gorgons have the power to erase entrants from time. Now, if you pay careful attention to Kabr's words as relayed by Pahanin, he describes the Vault in reverse sequence. It's almost as though he's not so much trying to penetrate the Vault as he is trying to escape it. I think that Kabr and his team attempt to seize the Vault, using the Aegis without understanding what it is. But when they confront Atheon the power of the Aegis fails and they are cast back through time. The full power of the Vault is brought against them and team members begin to succumb. Kabr makes a Faustian bargain and tries to use the power of the Vex against them. In doing this he gains understanding of the nature of the Vault and realizes that the Aegis failed in the end because his own victory would erase the timeline in which he created it. Using his "own Light and the thinking flesh of the Vex" he creates the Aegis, a means of seizing control of some portion of the causal loop mechanism underlying the Vault. Bereft of the protection of the Light, the Vex begin to corrupt and assimilate Kabr. Ghostless and fighting for his own sanity, Kabr faces his final Trial: the struggle to pass on the information necessary for other Guardians to take up the cause. With Pahanin as his messenger, he preserves hope for a future that cannot be rewritten to suit the Vex, but also sets in motion the events that lead to his own downfall.