The Golden Flame Inheritance was able to gauge whether Damian was ready to unlock the next thing from the inheritance from his body and mind.
Once the inheritance had confirmed that Damian wanted to cultivate externally and sensed that he had realised that Internal and External cultivation could be harmonised, he unlocked two things.
Damian was on the right track, but peak Mortal Cultivators in the country that had cultivated to the peak of the Mortal Cultivation Level both internally and externally, such as the king, had also found that they could be harmonised.
For Damian to notice that at the low cultivation that he was at and at his young age, showed how much of a young talent and prodigy he was in general, not only in terms of cultivation and combat.