The Six-Word Mantra is also known as the Heart-Centering Mantra.
Although Zhang Chen didn't know how the Six-Word Mantra could restrain the Great Freedom Celestial Demon, he understood from the demon's words that in the future, to completely control the Great Freedom Celestial Demon, he must start with the Six-Word Mantra.
His Light of the True God could only exterminate the Great Freedom Celestial Demon but couldn't control it; especially since in his Spiritual World, the mysterious Light of the True God couldn't even penetrate.
What use is it to slay a Great Freedom Celestial Demon's avatar? Who knows how many avatars this guy has? Moreover, with just a thought, an avatar could be reshaped anew.
