The bargain they reached was thus:
The Dreamer had committed sins of untold ugliness and depravity, sins that could not be atoned for because the Dreamer could not regret them. Infernus was the only possibility should the Dreamer die.
It was offered this escape: an eternal dream of light and beauty, populated by beings that were the echoes of the souls the Dreamer had destroyed in one way or another and were thus bound to it. In this place, the Dreamer would be all of them and none of them, with none of its sins and none of its vices. Its body, wasted and twisted but immortal, would be but a vessel.
Naturally, there was another side to the bargain, as there often is. In exchange for this private heaven apart from the blistering embrace of Infernus, the Dreamer agreed that if ever its physica body were destroyed, or if ever it were awakened from within the dream, it would immediately die and go to its just reward. The deal was sealed, and the Dreamer secreted itself in a well-guarded, obscure place of hiding.
And the dream-specters inhabiting its visions? Why, that is us. All of us.