The wordings that appear in tradition says:
كلنا واحد من نور واحد
(Bihar-ul-Anwar 26: 16 & 281)
It implies that they nurture from one source of light. In their original creation, they are from one light. In the world of spirits and shadow, their derivation is from one source leading to one truth. That “نور واحد ” one light refers to the light of Allah’s Greatness.
Traditions say that the souls or spirits of Imams (a.s.) are higher than“Elliyeen”  and their bodies from“Elliyeen” . The souls of Shias are from“Elliyeen” and their bodies lower than“Elliyeen” . Moreover, the programs and responsibilities of Imams (a.s.) all belong to the world of revelation and their beliefs, ethics and deed are all divine and human. Their main policy in life is perfect devotion and submission before the Almighty Allah even though their eras differ from one another and their duties varies from one another.
Thus, Imam-e-Zaman’s (a.t.f.s.) duty differs from all other Imams (a.s.), mainly due to his implementation of the Islamic commandments in the entire world.
Their appointment by Allah, and their immaculateness is something common in all of them. Also, all of them are medium or channels through which the living creatures derive benefits. Besides, they are all deeply rooted in knowledge and are interpreters of the holy Qur’an. Lastly, they bear the responsibility of safeguarding religion from heresy.