"The Spirit of Heavenly Fire... control the Heavenly Fire!!"
The reason why Heavenly Fire is feared, and why it can contend with ancient Divine Spirits, is because of the existence of the Heavenly Fire Spirit.
If Heavenly Fire were likened to a person, then the Fire Origin would be the body, and the Fire Spirit would be akin to the soul.
Without a soul, only a shell remains, and it has no fighting strength.
If there is a soul directing everything, then various secret techniques can be unleashed.
Just like with Heavenly Fire, without the Heavenly Fire Spirit and only the origin remaining, Lin Feng refining the Heavenly Fire would still face the instinctive resistance of Heavenly Fire, but it would not be too violent.
But if the Heavenly Fire Spirit were not dead, that would be another story entirely.
With the Heavenly Fire Spirit present, it could perhaps annihilate Lin Feng in an instant.