"See now, with prophetic eyes.
The Brood stirs...
The Ward falls...!
Utopia is undone...
Mark well this Prophecy of the Rifts:
We have chosen YOU to prevent the coming apocalypse.
Go with the grace of the Vigil!"
Do note, this is only part of the Prophecy of the Rifts: there is more as you complete the Saga Quests and begin to fulfill it.
At the very least, the Vigil can peer into other Slivers and determine if they desire that future or not. Such as NOT desiring a Terminus-esque future. The Fall of Lantern Hook is also a Sliver by the lore definition, you may remember. My theory is that something is blocking the Vigil Gods from directly intervening. The Messenger, at the very least, is able to exist in multiple realities at once, or otherwise clone herself (in Sanctum you can meet the Messenger of Tears, the Messenger of Bahralt, of Time, of Thedeor, of Sand, etc).