Blood Qi and spirit force were two major directions in the cultivation of Spirit Stream Realm cultivators. Being abundant in blood Qi meant having a robust physique, which was beneficial for cultivators of all sects, while spirit force was fundamental for cultivators engaging in combat.
The speed of flow of both elements directly related to the strength of a cultivator.
Why would a cultivator become much stronger after switching to a Heaven Rank technique? First, because after adopting a Heaven Rank technique, the control over one's spirit force improved greatly. Second, the speed at which the spirit force flowed within the body also underwent a qualitative change.
This royal jelly could enhance the flow speed of blood Qi and spirit force, effectively strengthening the physique of physique cultivators while also enhancing the strength of the cultivator.