Lin Shen followed Tie to learn Lawless Heaven. According to Tie, one must first be able to feel the existence of the Order Law before breaking it.
To have laws and to break them, that's Lawless Heaven.
To not even perceive laws and to act recklessly, that's not Lawless Heaven but rather the fearlessness of the ignorant.
Thus, the first task in Lin Shen's studies was to perceive the Order Law. A Nirvana Being could sense the Law Power, as long as they didn't attempt to control and merge with the Law Power, they wouldn't advance to Immortal.
At the Nirvana Level, the more laws one discerned clearly, or if one sensed some laws that others couldn't, the stronger one might become when reaching Immortality.
Sensing the laws of others would generally only culminate in Past Law, but this was a process everyone had to experience.
If you couldn't even sense the laws of others, it would be even more difficult to sense those laws yet to be discovered by anyone.