The Reasoning behind The Sundering? (*6.0 Endwalker Spoilers*)

[Lyth]

Yes, but they couldn't do so bodily. So how could Hydaelyn go to the First and then come back?

It's probably not all that different from how Elidibus summons Ardbert and the Warriors of Darkness to the Source during the events of Heavensward. After all, we know that Minfilia heads back to the First with Ardbert, Branden, Renda-Rae, Nyelbert, and Lamitt during the events of 'One Life for One World.' (Heavensward), where they hold the fort until the events of Shadowbringers.

In 'The Word of the Mother' (Heavensward), Krile explains that a particular aetheric signature shows up both at the Isle of Val, which Krile escaped with Hydaelyn's help, as well as the Sil'dih Aqueducts when you were escaping Ul'dah, where Minfilia disappeared. Krile speculated even back then that 'Hydaelyn may have the capacity to summon the consciousness of gifted individuals to her side.' Now where have I heard that one before? She then hangs out in the Aetheric Sea with Hydaelyn until Urianger hatches his plot to give Minfilia and Ardbert the energy needed to go back to the First. Hydaelyn's connection to the individual shards is probably that they're all linked through the Aetheric sea and her ability to move people around is linked to the fact that she was formerly Azem. I'm not sure how the Ascians do it, however.