It's been a while since we last tried to discuss Belladonna's plans. This is my idea of what it could be:
What was just delivered to her could be an artifact that could seal the city in a dark dome, where no one from heaven could get into it if they're not already inside. Here, Belladonna could prepare her army on the surface without interference for an invasion to conquer the earth.
The only catch for any story, Blight, who's been her active silent partner, is going to betray her...