To be Sages in the Untainted Land, one definitely needed Merits. Although one's Merits could not be withdrawn, his capacity would be influenced negatively if he carried Karma on his back. Further, a certain amount of Karma would turn a Sage into a common figure. As for Zhenyuanzi, his attack obviously hit Houtu's Achilles heel.
Now it was totally impossible for Houtu to fight back even though she wanted to do so since the Nether World Book Formation set by Zhenyuanzi was connecting more and more ley lines on Untainted Land. That was to say, if she really killed Hongyun and Zhenyuanzi, the Karma she would carry on could possibly turn herself into a common figure and the entire Wu Tribe might also face extermination.
However, Houtu was still not willing to just let Zhenyuanzi and Hongyun go like that, so he could only say, "Zhenyuanzi, you're right, while I, a Sage, have many methods to torture you. Even though I can't kill you now, I can let you be sealed eternally."
