After everyone had their spells completed and the research done, they reconvened in the Sanctuary. This would likely be the last meeting before the attack, and preparations were to be made upon it's completion. The scelesti were going down. Hard.
Or at least that was Leo's hope. In truth they needed to plan, establish roles, get their shit in perfect order. This conversation was required, and it was going to happen in a constructive manner if Leo had to respectfully ask Ariadne to brainwash the others to make it happen.