We call them Soul Devices. When a person with enough spiritual power comes within proximity of the spirit realm, or the "Eclipse", and possesses a degree of willpower- a Soul Device may manifest. They're special weapons that forms and capabilities vary from person to person. There's some differences here and there ... but just like Visions, their cores are powered by different types elemental energies that are commonly found in our spirit realm.

I admit, there's a lot we still don't know about Soul Devices, but I can confirm they don't come from the gods.

[So there's that]

Though if Celestia is responsible for Visions, I don't think they're a way to weed out threats. Otherwise, Vision Hunt Decrees would be found in the other nations. This seems to be an Inazuma specific issue.