Though they were once part of the One Great, Elden Ring's Frenzied Flame split from the Greater Will because it believed that the Greater Will made a mistake, and now seeks to make all that was split apart whole again. This, in turn, led to the Two Fingers and Three Fingers being split rather than remaining a whole hand. This adds the Greater Will and Frenzied Flame to the list of characters or ideas in Elden Ring that represent opposing ideas, yet are two halves of one whole.
[Warning: This article contains spoilers for Elden Ring.]
Elden Ring puts the player in the role of the Tarnished, somebody who was once robbed of their Grace and exiled from the land in the hope they would grow stronger through strife. Though it is hardly the only Outer God interested in the Lands Between, the Greater Will has the highest degree of control in the land out of the Outer Gods. As the Tarnished roams the world of Elden Ring's Lands Between and interacts with its inhabitants, they can learn why the Frenzied Flame and Greater Will split, with the messengers of its will - the Three Fingers and Two Fingers, respectively - also splitting from what was once a whole hand.
While Elden Ring makes it easier to find information about the Two Fingers than the Three Fingers, the Tarnished can learn some crucial information about the Three Fingers from Elden Ring's Frenzied Flame, disagreeing with the actions of the Greater Will, wishes to destroy the world by burning it so that all will be One again. Much like the 
Law of Regression and 
Law of Causality , the Greater Will and Frenzied Flame represent two opposing halves of the same whole - a theme that can be found throughout all of Elden Ring.
Elden Ring - The Three Fingers And The Frenzied Flame
The description of the Law of Regression Incantation reads, "Regression is the pull of meaning; that all things yearn eternally to converge." This fits in with both Hyetta's words and the Lord of Frenzied Flame ending. Unlike Two Fingers, which are found at the top of Divine Towers, the Three Fingers is found underground. It includes the thumb, index finger, and middle finger with veins of light running through it, allowing it to grab the Tarnished and burn fingerprints onto their flesh. This locks the Tarnished into the Lord of Frenzied Flame Ending, where the wish of the Frenzied Flame is granted and the Lands Between is burned away, unless the Tarnished acquires and uses Miquella's Needle from Malenia in Elden Ring.
Since the Frenzied Flame has opposing views to the Greater Will, it comes as no surprise that as the One Great began to fracture, the Frenzied Flame split from the Greater Will. Elden Ring doesn't give a clear explanation as to when these Outer Gods split, or why they both chose for their method of communication with the Lands Between to be half of a hand. While it could be a purely symbolic choice to show a connection between the opposing Greater Will and Frenzied Flame, it could instead have a lore meaning that players have yet to discover. Perhaps the split of the Two Fingers and Three Fingers occurred more recently than it may seem.
Elden Ring - The Two Fingers And The Greater Will
The Greater Will, in contrast to the Frenzied Flame, fits the description of the Law of Causality, which reads, "Causality is the pull between meanings; that which links all things in a chain of relation." The journey of the Tarnished through the Lands Between shows the chain of events that the Greater Will's reign has caused. Elden Ring's Outer Gods reside in the Cosmos, so they need servants to carry out their will for them. With the knowledge of their goals that is available, it's easy to see why the Greater Will is able to recruit the most servants and hold the majority of power in the Lands Between. Unlike the Frenzied Flame, the Greater Will offers more tangible rewards in exchange for obedience, such as godhood and the power of the Elden Ring. The Greater Will also gives Grace to those living in the Lands Between, even calling back the Tarnished, whose Grace was stolen by Queen Marika, to return to the Lands Between and aid in the restoration of the Elden Ring.
Hyetta tells the Tarnished that the Greater Will's mistake was the catalyst for the splitting of the Two Fingers and Three Fingers, with the ring finger and pinky becoming the envoy for the Greater Will. She says, "But the Greater Will made a mistake. Torment, despair, affliction... every sin, every curse. Every one, born of the mistake." This could refer to the Greater Will bringing Destined Death to Elden Ring's Lands Between as being the mistake, or that making Marika the vessel of the Elden Ring was the mistake because she believed that suffering built strength. Perhaps the mistake was made long ago and was unrelated to the Lands Between. Regardless of the nature of the Greater Will's mistake, the Frenzied Flame believes the only way to rectify it is to burn the world so that it will once more become one.
Whether it's intended to be symbolic or literal, the splitting of the Two Fingers and Three Fingers follows an important pattern in Elden Ring - a pattern where one whole splits into halves, or halves unite to form one whole. Far from being the only beings that have split, the Greater Will and Frenzied Flame are the only Outer Gods seen to fit this pattern. Although FromSoftware creates games with intricate lore and clear answers are difficult to find, players may find answers to their questions about what lies beyond the Cosmos one day, especially if Elden Ring receives an Outer Gods DLC.
