Eremiel is an angel that was created by God to guard the souls of the underworld. He wasn't created to alleviate their situation or their punishment. Rather, he is to act as a guardian over these souls should anybody conjure them forth or need to communicate with them for whatever reason. As such, when you have this piece you will gain the powers of Eremiel. You will speak with his authority and you will be able to conjure forth any soul that you wish to communicate with. Now, since Eremiel is an angel and he is also the angel of the souls in the underworld, this piece will allow you to call forth and communicate with souls from both Heaven and Hell. You can simply use this piece to communicate with a lost loved one. You can also use the powers of Eremiel to summon souls from which you want to gain secrets or magic. These souls will hand over their secrets and secret magic because you are speaking with the authority of the angel who has full authority over souls.
