This could be to remove them as attackers or blockers in combat , or to give them summoning sickness and prevent them from attacking that turn
Often, a cards flavor text consists of a few sentences or a quote to highlight whats going on in the setting, the cards art, or the mechanics of the card itself
How Many Proxies Are Too Many
Enchanted permanent is indestructible
One thing that we learned from the original Modern Horizons was that, while Modern Horizons absolutely appealed to Modern players, it had much wider reach as well
As for the storyline, visually, Ob Nixilis and Nahiri have been our only short reprieves from this threat since Origins, but both interacted with the Eldrazi in some way