"Treasure every moment, every step of your descent, and there in the depths where souls and stars rest, find your truth" - Emet-Selch Endwalker Launch trailer
Hythlodeaus during "Etched in the stars"
"Heh heh... I see you have been collecting stars.
I speak of those crystals. They have constellations etched upon them, yes?
High in the heavens, those stars shine their guiding light down upon the lives below. Fitting symbols for the Convocation of Fourteen, would you not agree?
As you will have gathered, each crystal bears an account of the life of a member of the Convocation as remembered by the unsundered.
Lest you worry, they aren't concepts; they are far too incomplete to be so. But they suffice for imbuing memories within sundered souls, that they might be restored to their office.
Keep them. I am sure Emet-Selch wouldn't mind."
Continued:
Among all the offices, the Fourteenth was most unusual. For while the rest sat in Amaurot, its holder was charged with gaining an intimate knowledge of the wider world.
In the course of his duty, he traveled the length and breadth of every land, and befriended countless folk.
He encountered troubles too, of course. Matters which he could simply have referred to the Convocation. But that was not his way.
Nay, more often than not, he would call upon his comrades, and together resolve matters themselves.
Such is the magick sealed within that crystal─the magick to summon the stars to your side.
In time of greatest need, should you wish upon it with all your heart, it will surely answer your call."
My guess is that the truth Emet-Selch is implying that we must find is the truth of the ancient world and the final wish of the ancients that Yoshida teased back in the fanfest. The launch trailer blessed us with quite a bit Meteor interacting with Amaurot as well which could be a clue to what EW holds.
Gripping the Azem Crystal:
Wishing Upon the Crystal:
Surrounded by Ascian masks:
Surrounded by Ancients:
Maybe we're supposed to take the Seat of Sacrifice lines:
"Herein I commit the chronicle of the traveler. Shepherd to the stars in the dark. Though the world be sundered and our souls set adrift, where you walk, my dearest friend, fate shall surely follow. For yours is the Fourteenth seat—the seat of Azem." literally. As the inheritor of the crystal we will sheperd the souls, memories and dreams of the departed convocation personally.
But that's just my long winded and personal interpretation