Could you please explain the necessity of Imam in simple words?

At the time of Imam al-Sādiq some of the Imam’s close companions like, Muhammad bin No‘mān, Hishām bin Sālim, and Tayyār were in the presence of the Imam.  Among them was also a young and a very clever man who was named Hishām bin al-Hakam. The Imam, addressed Hishām bin al-Hakam and said to him,

 “O Hishām! Don’t you inform us about what you did with ‘Amr bin ‘Ubaid and how you discussed with him?”

Hishām replied, “O the son of the Prophet! I render you as a very great man and I am ashamed to talk in your presence so much that I feel I could not talk correctly.”

The Imam again told him, “When I commanded you, you had better comply with it.”

Here, Hishām started talking and said, “I was informed that ‘Amr bin ‘Ubaid (who was a Sunni man and did not accept the Imamate of Imam al-Sādiq) used to hold a circle of discussion in the mosque of Basra. I decided to go to Basra to participate in his session. I travelled from Kufa and arrived there when it was Friday. When I went into the Mosque I saw ‘Amr sitting in the middle of a large group of people and they asked him some questions. I sat at the end of the crowd, stood on my knees and told him, ‘I am a stranger. Do you permit me to ask?’ He replied, ‘Yes.’

I asked him, “‘Do you have eyes?’ He replied, ‘My dear son! What kind of question is this? Why do you ask about something that you clearly see?’ I said, ‘My question is just this. Do you have eyes?’ ‘Amr said, ‘Yes, I have eyes, though your question was silly.’ I asked again, ‘What do you do with your eyes?’ He said, ‘By the help of it, I am able to see colors and people.’”

I once more asked, “‘Do you have nose?’ He said, ‘Yes.’ I asked, ‘What kind of job do you do with it?’ He replied, ‘With it, I can smell’”

Here Hishām continued asking ‘Amr about his mouth and his ears and their usage and ‘Amr answered him.

Then Hishām added, “I asked him, ‘Do you have brain?’ He said, ‘Yes.’ I said, ‘What do you do with it?’ He said, ‘I can check the trueness of what is sensed by my senses.’ I said, ‘Doesn’t your other body parts suffice you from your brain?’ He replied, ‘No.’ I then asked, ‘How could not they suffice you from your brain while they are sound and healthy?’ He replied, ‘My dear son! When my senses feel something, they refer it to my brain to obtain certainty and to remove doubts.’ Here I confirmed what he said, and asked, ‘Then Allah appointed the brain to discard the doubts of the other parts; otherwise your body parts could not obtain certainty.’ He answered, ‘Yes.’”

Here Hishām continued, “At the moment, I asked him, O Abā Marwān! Allah the Exalted, the Glorified did not leave your body parts without a leader and appointed for them an Imam to correct for them what should be corrected and to make them certain about what they doubt, then is it fair for Allah to leave all of these people alone to live in perplexity and doubts and disagreement and does not appoint an Imam for them to refer to him in order to remove their doubts?’”

‘Amr remained silent for a while and then looked at me and said, “’Where are you from?’ I said, ‘from Kufa’ ‘Amr immediately said, ‘Then you are Hishām bin Hakam!’”

Here Hishām continued, “‘Amr came to me, hold me, placed me where he was sitting, went to a cornerm and didn’t say anything till I started to go.”

Here Imam al-Sādiq smiled and said,  “Oh Hishām! Who taught you this knowledge?”

Hishām replied, ‘It was something that I learned from you.’ Then the Imam continued, “By Allah it was written in the books of Abraham and Moses.”^[1]