If things progressed normally, Lex would need to reach the very peak of the Celestial Immortal realm before he could safely learn about matters pertaining to Dao. At that point, his cultivation was no longer a level acquired through absorbing energy or cultivating his technique - it was about the depth of his understanding of laws.
Starting all the way from Foundational Laws, to Relational Laws all the way to the eight Ruling laws, he needed a deep and thorough understanding of each of them independently as well as how they interacted with each other. Only then would he be able to reach the ninth level of the Celestial Immortal realm.
That, then, would serve as the foundation upon which he could learn about Dao, not to mention it would strengthen him enough to allow him to tolerate that knowledge.
Now, however, an external barrier suddenly enveloped his mind and soul, protecting him and allowing him to touch upon the topic of Dao, even if it was ever so briefly.
