The spirit qi had gotten increasingly thick under the blood-colored night. The closer he got to a certain place, the thicker it became.
That was the place where the Spiritual Eye of the Spiritual Tide was that particular time.
That was also where the Spiritual Eye was that Lu Xuan remembered it to be, back when the world was being restored as such for the first time.
Lu Xuan would have required the Spiritual Eye if he were to make his next breakthrough. Great amounts of Spirit Qi would have been unleashed on that day of the Spiritual Tide. That would have allowed Lu Xuan to progress much faster than if he were to just train on his own.
At the moment, Lu Xuan's powers were far greater than it had been when he had just been reincarnated. He would have required a lot more Spirit Qi if he were to make the breakthrough in one shot.