Acceptance Soul can create a special space in your body which is used to store a Heavenly Flame. After all, if you have not completely refined the flame, the kind of destructive ability of a Heavenly Flame would incinerate everything, including your vortex and body, except this kind of space of nothingness.
However, an Acceptance Soul is very rare. It also has some relationship with the storage rings. An Acceptance Soul can only be found at the center of the highest grade Storage Stone which makes Storage Rings. You should know that the highest grade Storage Stone is the essential raw material in smelting a high-grade storage ring, so its rarity can be imagined. The presence of an Acceptance Soul in a high-grade Acceptance Stone is not very high. Now you should know the extent of the rarity of an Acceptance Soul.