Spirit was dull.
Spirit was dull like dry toast; like that dry toast, sure, that symbolized the unity of the divine and mortal spirit in the self-the dry toast of Horus' descent into the underworld, the dry toast of Marduk conquering Tiamat who was the fleshy body of the world, the dry toast of the Resurrection, if the Christians will forgive me-the Incarnation, the Unity, the Glory numinous in the world-
But toast, still and butterless.
It was yin, but it was yin not just in the sense that yin is in all things, but yin in the sense of lurking damply, darkly, stillnessly on your character sheet, not stirring even when you invoked it to grit the teeth of your Auctoritas against your foes.
So now it has gone the way of all things, which is to say, back to the dictionaries and liquors and previous editions that are the word Spirit's natural home.
Instead there is a yin that coils around itself and bites its tail and surges with a divine fire of stillness; or, at least, a yin that you use for stuff in play, even if it's still a gentler power than Domain.
Really I'm not sure how to do a good spoilers thread without having to mediate between the threat of breaking an NDA and wanting to say as much as possible; do I just like tell people stuff here? Nah, that'd be bad. So instead I shall write at random and pretend the Spirit hath given meaning to the words. ^_^
TL;DR: Persona is something you use to do generally quietly cool things, as opposed to the quietly cool Attribute that was Spirit.