What is the requirement of a Muslim in affirming that Prophet Muhammad (ﷺ) is Allah’s Messenger?

When we say, ‘’Wa-ashadu anna Muhammadan rasulullah’’ – And I bear witness that Muhammad is the last messenger of Allah, this is a commitment to follow his instructions; to follow primarily the Madhab of Rasulullah (ﷺ). That is what it is - a commitment. That he is the only one whom we should follow blindly unquestioningly. We would not compare what he said with what we think to be reasonable and decide that what is reasonable is better than what he said. We would not find ourselves in that situation.

Anybody else who has made rulings, has made decisions, has given opinions; anybody else is subject to questioning using our reasoning; “This doesn’t make sense?”, “Let me hear somebody else’s opinion”, “Maybe this is not correct or may be this is a mistake?”

All of these are reasonable doubts and feelings that we can have for anybody, even it is Imam so-and-so or Imam whoever. He was a human being and he could and would make mistakes.

If we say that Imam so-and-so is 100% accurate and he can never make a mistake,  we have destroyed ourselves and have become undermined. In fact, we have violated our commitment to follow only Rasulullah (ﷺ) blindly.