Can you remind me what that was? It's been a while since I played Azure, and the plans always feel a little nonsensical.
Well, I feel like the plan is a little nonsensical no matter how you look at it but basically:
The stuff that's going on in Crossbell during Azure with the Azure-Zero project, and I think specifically the appearance of the Azure Tree, causes mana/magical energy/whatever to surge through the ground in Crossbell and neighboring countries. For reasons(???), gaining access to the Sept-Terrion in Erebonia requires lots of magical energy, a condition which is now met and allows for things like the appearance of the Infernal Castle and the activation of whatever ritual occurs when the Divine Knights fight each other.
I guess why all those things matter for accessing the Sept-Terrion is something that's elaborated on in CS3 and the beginning of CS4 Act 2, but basically my understanding is that the Divine Knights are fractured pieces of the two Sept-Terrions and that this ritual allows them to fuse together...or something. ---
I didn't do guru this year but azuarc can be in my sig anyways.