F&Q:

What is the method of applying the “principle of grace” with the existence of the concealed Imam?

Appointment and specification of the Imam by Allah is grace, and grace is obligatory upon Allah. Therefore, Allah has appointed someone to Imamah after Imam Hasan al-‘Askari (peace be upon him), and that person will not be other than his son, since the incapacity and invalidity of the other claimants to Imamah has been established and at present, no one has such a claim.