Thanks for the opportunity!
The premise is as follows in the current state of my theory:
Life must leave to develop elsewhere, whatever it takes. That is its nature as a cosmic wanderer.
Not so creepy at first sight, is it?
Let me elaborate a bit.
As life has no physical form of its own that would allow it to accomplish its will directly, it uses spiritual energy to influence its creations (Cetras, plants, animals,...) in order to achieve its goal. It can talk to them (in a way that is difficult to explain according to Aerith) because it can manipulate this energy. These creations thus inherit a kind of destiny as they will be subtly guided in a direction defined in advance.
The consequences of what the stream pushes them to do will certainly lead them to refuse the mission as their beloved environment and also their consciousnesses will be swept away (Chaos must precede departure).
So they should not realise what they are actually doing and if they think that their choices and actions make them heroes it will be easier ("Unattainable dreams are the best kind." Lazard).
In my opinion, the ultimate role of the party will be to trigger the propulsion of the meteor on which the Lifestream will have taken place. (
theory).
Influencing behind the scenes is certainly not an easy task, and it has to be done through memory transfers and manipulation of souvenirs. In particular, it'll have to manage to break Cloud's mind so that he brings the Black Materia, and then repair his mind so that he can resume his place as a hero and continue his mission.
Manipulating memories can be a powerful tool. But inconsistencies are bound to arise, and these inconsistencies may have been staged to give an attentive player the opportunity to see the other side. I think that would be the case with the sequence in the Lifestream but also in some others.
This concept of hidden reality would remind me of Plato's allegory of the cave and Sephiroth's tirade in the Remake:
"Those who look with clouded eyes see nothing but shadows."
"All born are bound to her."
"Should this world be unmade, so too shall her children."
Anyway, this is the framework that is supposed to make sense of my ramblings.
I have no intention of trolling, I'm just trying to acknowledge the work of the developers.