(2) Must be inviolable to error and sin both in deeds and speech...

(2) Must be inviolable to error and sin both in deeds and speech, because sinfulness has no effect in propagation. People do not esteem the speech of a person whose manner and speech are at odds. They even take his deeds for his mendacity and imposture by saying if he meant what he said, he would act accordingly. By bringing these two aspects together in one phrase, we can say that a prophet must be inviolable to errors and sins to render preaching and propagation effective.

In His words, the Almighty Allah, too, refers to this point and states: "The Knower of the unseen! so He does not reveal His secrets to any, except to him whom He chooses as a messenger. for surely He makes a guard to march before him and after him, so that He may know…