There are three ways for reaching the nafsul-amr religion:
1- Revelation
2- Narration
3- Intellect
Normal people can only reach true religion using the second and third method, while special people can also reach it via the first.
There are three ways for such a thing to take place:
1- When Allah (swt) unveils a portion of it. The prophets are the only ones who possess the potential to become aware of some or all of the “nafsul-amr” religion using this method.
2- When what has been unveiled by Allah (swt) is told and narrated to others.
3- When the mind and intellect reaches some of its teachings and elements using the specific ways there are for such a task.
Therefore, normal people have two ways to find out about the nafsul-amr religion; narration and intellect and only a special group can use the first. The only difference is that there are always possibilities of mistakes taking place in the second two, while mistake has no way in the first.
For further information, see:
Mahdi Hadavi Tehrani, Velayat va Diyanat, The Cultural