Gu Chensha's words were very clear.
He wanted Nannan to see that if she did not make a choice, there would only be one outcome; everyone she cared about would die.
So, Gu Chensha was not threatening Su Mu with Nannan, but threatening Nannan with Su Mu!
....
"If I'm not mistaken... you haven't fully refined the River of Time."
Gu Chensha stood with his hands behind his back, smiling as he spoke to Su Mu.
As long as Su Mu has not fully refined the River of Time, he is destined not to be his match; all cultivation realms are meaningless symbols in his eyes.
...
Su Mu couldn't discern Gu Chensha's strength not because Gu Chensha's cultivation realm was too high, but because Gu Chensha didn't have any cultivation at all!
