:The second reason is the necessity of knowing the Imam of each era

"It is a sign of faith"

 Aban ibn Taghlib says: I asked Imam Sadiq: Is a person faithful if he knows all Imams except for the Imam of his own era? The Imam said: “No.” I asked again: Is he considered as a Muslim

The Imam answered: Yes

The Source: Kamal al-Din and Tamam Al-Nimeh

  :The important lesson

"Every Muslim is not considered as a faithful one"