This was the Heart of Fire. Lin Feng originally did not have the "innate ability" for flames, but he had the Chaotic Origin Stone. Relying on the "affinity" between the Chaotic Origin Stone and the Rule of Fire, Lin Feng forcefully obtained the "natural ability" for flames, and condensed the Heart of Fire.
Once the Heart of Fire was formed, it could continuously absorb flames from the Chaos. They would be transformed to the famed Chaotic flames by the Heart of Fire.
This was how the Incendium True Scripture worked. It used Chaotic flames as the foundation for cultivation. Lin Feng did not need to cultivate the Incendium True Scripture. He only needed to cultivate the Chaotic flames.
Actually, there were also differences in the level of the Heart of Fire. At the highest level, the Heart of Fire was very efficient in absorbing and converting Chaotic flames. On the other hand, low-level Heart of Fire could only barely absorb and convert Chaotic flames, so the efficiency was very low.
