La Persona Superiore a Dio is Italian for The One Above God and is one of the highest reachable statuses on the magic side. The ultimate goal of God's Right Seat is to achieve this state by diluting the original sin they hold as humans as much as possible. The purging of original sin allows those of God's Right Seat to use the normally unusable spells regarding God and the angels. The groups goal is to sit on the Right Seat of God as sitting to the right of someone in christian symbolism is to have the same status as the being they wish to share that status with. However this is only a stepping stone to achieve the existence of The One Above God. Fiamma has the sole power to attain the status because he represents Archangel Michael who currently occupies the Right Seat of God. When Fiamma reaches La Persona Superiore a Dio briefly, he becomes the core of the legend and gains the ability to reproduce all the miracles in Christianity as opposed to the ones just designated to the right hand.

““Currently, they are aiming for Michael, the being with the highest-level power who was created to oppose Lucifer.” Lidvia’s voice was uniform. “Lucifer is the only being that has ever been allowed to sit to the right side of God. And Michael, who defeated Lucifer and became the ruler of all the angels, is a higher being than Lucifer, who was once his equal. Or so God’s Right Seat believes.” The right side. In the Christian Church, that position indicated equivalency. The first Christian martyr, Stephen, used the word “right” when honoring god to indicate that the Son of God was an equivalent existence to God. He used the word “right” in that way because, according to the concept of the trinity, God and the Son of God were honored as equal. But what about an angel? Why was Lucifer able to sit to the right side of God? And did Michael really have such enormous power that he could defeat an archangel that sat to the right side of God? Since God was a unique being and was the greatest being in the world, there should be no one sitting in that “equivalent” right seat. Not to mention that it was hard to think that God would give that seat to one of the angels he had created as a tool and a servant. They must have been thinking that there was some special meaning in the fact that an angel, a lower being, was given that seat even so. “The group was created with the goal of sitting in God’s Right Seat. And they believe that once they are in the Right Seat they will be able to use that power to evolve into an existence different again from an angel.” The name of that existence was... “La persona superiore a Dio.” Both Stiyl and Agnese frowned upon hearing those words. In other words... “The One Above God. That is what I hear it is called.””
(To Aru Majutsu no Index Volume 14, pg 181-182)

““But because they have incompletely eliminated their ‘sin’, they can carry out spells of a level surpassing what normal people can. It is said that they can even use the normally unusable spells that deal with the angels and the Lord.” If they succeeded in that, God’s Right Seat would truly be able to freely use the spells of the angels. And once they could do that it was possible that not even a saint would be able to stop them.”
(To Aru Majutsu no Index Volume 14, pg 66)

“The Right Hand which creates all miracles will destroy all evil. The power of the Right sent the Lord of Devils into Hell and ensured there he would be bound for one-thousand years. If I can completely master the Holy Right... are you not curious as to what is inside it?” “Don’t tell me...” [...] “If it’s me, it can be mastered.” Fiamma laughed and moved his right hand horizontal to himself. As if responding to his command, the third arm splitting the air moved as well, mimicking Fiamma’s actions. “If it’s The Likeness of God, it can be mastered.”
(To Aru Majutsu no Index Volume 16, pg 197)

“The power that resides within me cannot show off 100% of its power except by way of your right hand. Imagine Breaker must be a type of purification tool the holy right hand naturally possesses, but to me it is no more than a mouse eating away at food stores. [...] If I wield the power that should originally have been within me at its full output, the salvation of all will be complete. After all, my arm possesses the power to save the entire world. People may refer to that as being The One Above God, but... I do not particularly care about that. I do not intend to match or exceed him. I only intend to gather all the power I have now and to save the world with it.”
(To Aru Majutsu no Index Volume 22, pg 47)