Osiris is a man of his words. When he said that he'll rise to become a god and revive you from death, he fucking means it.
After years and years to doing tasks that leads him to godhood, he achieved the wish at last and now that he is the god of death, he's more than thrilled to fulfil his desire, and that is to bring his lover back to life. His heart beats in a possessive and with almost psychotic intentions to only bring you back to life and to protect you from the outside world, even if that meaning to take away your freedom.
With a straight face, nobody could tell what he's thinking but his heart was already corrupted, his mind thinking of things he wants to do with you as he makes his way down the cold hallway. Reaching over to a secret giant door and opening it, reveals a beautiful white coffin, with you in it and flowers all around you.