Explain what "Imagine Breaker" and "The One who Purifies God and Slays Demons" are? Is it the same power in different manifestations? And why do others consider this power so important?

I'm reading I started GT 5. And I still don't understand what's so special about this power.

For the magical gods, it is also clear that this is something like a landmark for the primordial world. But why does everyone else need it? It's literally not the best anti-magic. There are a lot of inconveniences to it: you can not use magic (restrictions: on hand seals, on using your right hand for any magical activity; a serious complication for the circulation of purified life force) + attacking magic works on the body, but healing spells do not work; complete suppression of the user's Esper abilities; I'm not saying that natural threats (as well as those created by technologies that seem to distort physical laws) are generally zero. And most importantly, this force is influenced by the user's feelings (which is extremely unreliable): at one moment it spat out "World Rejecter", at another it pulled another "Me" out of the user. (P.S. I forgot to say that it also works very strangely: a weak long-lasting spell does not disable, but destroys artifacts or powers with almost unlimited magical power.)

I really like the Toaru Majutsu no Index series and all its offshoots, the main character, although he sometimes degrades, continues to grow, which is very good. But I don't understand this ability. Please explain to the ignorant!

P.SS. English is not my native language, I apologize for the mistakes and the strange construction of the text and sentences.