The reason Jiang Chengxuan took out the Spiritual Treasure Advancement Talisman was to see if it could upgrade his heaven-connecting spiritual treasure, the Five Elements Diagram.
However, it turned out that the talisman couldn't be used for advancing a heaven-connecting spiritual treasure.
With no other choice, Jiang Chengxuan decided to save the talisman for later use on Shen Ruyan's Five Lightning Immortal Slayer.
Yet, the divine power upgrade opportunity could be applied to any of his divine powers without hesitation.
He chose to enhance his intrinsic divine power, the Five-Color Divine Light.
In just an instant, Jiang Chengxuan distinctly felt the power of his Five-Color Divine Light increase manifold over its original strength.
If previously he was uncertain about the effectiveness of his Five-Color Divine Light against Immortals, now he was confident that it could affect them just as well.