In order to restrain the devils in this realm, Serefina had to find the way how to bring them to the realm that even Hope was not aware until recently.
And things only got complicated when Serefina found out there were only two ways to make it happen.
It was either Hope, who needed to bring the seven devils to this place using her power, or the devils could enter this realm willingly, like how Lucifer had been lured here.
For the first option, it was clear to see that Hope couldn't handle the seven devils altogether when she didn't even know how to use her power potentially, neither did Serefina.
Therefore, Serefina took a big risk and stole the power from all the guardian angels, but it didn't mean all of this had happened without any side issues.
The power that Serefina stole from the guardian angels was very pure, it clashed with her own power which made it hard for her to contain them both effectively.
