There are some details that attracted my attention while playing.
1) why Corypheus needed to sacrifice the Divine to become a God and not another person?
2) There's Leliana's relationship with Justinia and the way Justinia saved Leliana by sending her subordinates.
3) When Inquisitor asks why Leliana cannot join to his party, Leliana says if she leaves her post she'd be "bound and blinded" without her spies.
4) Leliana heard voices and saw visions that once told her to follow the Warden.
Needs more explaining? Here;
1) I think Justinia was carrying Andruil (The Elven Goddess of Sacrifice and Hunting) in her just as Flemeth carried Mythal in her. In Elven Legends it is said Ghilan'nain the God of Halla (later we find out she was actually god of all animals) was once a mortal woman. She rose to Godhood after making sacrifices to Andruil and to the other Gods with the help of Andruil so other Gods did not object either. Sacrifice, Andruil and becoming a God.
2-3) It is said, Ghilan'nain was once captured by a hunter but Ghilan'nain cursed hunter so he couldn't kill/hunt anything anyomre in order to save herself. After trying and failing to kill Ghilan'nain or any of the animals, hunter got angry and "bound and blinded" Ghilan'nain and left her to die. Ghilan'nain cried for help and Andruil sent her hares and they chewed through the ropes that bound her, but Ghilan'nain was still wounded and blind, and could not find her way home. So Andruil turned her into a halla (the symbol of purity). In DAO: Leliana's Song, Leliana was captured and put in a dark prison after being betrayed by Marjolaine. Divine Justinia sends her the cloistered sisters to get her out of that prison but Leliana was still a rogue, an assassin so she was "blind". Justinia told her about the chantry and the maker and turned her into a cloistered sister. So, she sacrificed all other abilities and talents (rogue, bard, assassin abilities like killing, seducing, lying) of her other than her purity, just like Ghilan'nain sacrificed all other animals other than Halla to become a God.
Another interesting detail; Andruil and Ghilan'nain were said to be "close". Justinia and Leliana are said to be "close" as well. When Inquisitor asks Leliana if they were close in a romantic way, she says something like "people always think of it when they hear two people are close, we were more than friends in another way,"
4) The voices Leliana heard and the visions she saw probably came from Ghilan'nain. We know that souls of gods and spirits/demons that people carry can whisper to them and show them visions.
So what we saw in the Fade might be the soul of Andruil, mimicking her last vessel. That would explain why Corypheus wanted to "sacrifice" the Divine to unlock the Orb and become a God. Even Fenharel couldn't unlock the Orb since he was recently awakened, I don't think just a spirit of faith could, in any way, unlock it.