So I haven't seen many people discuss the Seventh Verse of the Divine Chronicles that Yoshida put up when he took charge. Urianger recites the first part in game as well:

Ne'er till land consumes sun can sea bear moons,
Heavens spew crimson flame, hells seep black dooms.
Stray seeds quicken in ash's grey embrace,
Valiant blades forged under the Twelve's good grace.
The first line appears to concern the change from Astral era to Umbral era, like from day to night.

We've seen the heavens spew flame in the first cutscene for each city, as well as in the intro video. I'm not sure what "hells seep black dooms" refers to though.

The third line seems to be talking about what happens afterward. Stray seeds quicken (us) in ash's grey embrace (post-impact).

The last line may just be looking toward the future. Adventurers (valiant blades) growing stronger after being saved by the Twelve.

However that's all just my first interpretation of it. I'd like to hear the input of others of course.