71. This (verse 56) was meant to comfort the Prophet (peace be upon him) and to warn the disbelievers who opposed him and obstructed his work, as if to say: Your duty is only to convey the message of good news to the people and to warn them of the consequences of disbelief. You are not responsible as to whether they accept your message or reject it, or to reward the believers and punish the disbelievers.
Such words occur in the Quran at other places also and are obviously directed to the disbelievers, as if to say: The message of the Prophet is meant to reform the people without any tinge of selfishness. As he does not force the people to accept his message, there is no reason why you should feel offended. If you accept the message, it will be for your own good, and if you reject it, you will be harming yourselves alone. For after conveying the message, he is relieved of his duty and responsibility; then the matter will be between you and Us.
Although this is a very simple and clear interpretation of (verse 56) (and of similar other verses), yet some people erroneously conclude from it that the only duty and responsibility of the Prophet (peace be upon him) is to convey the message and nothing else. They forget that the Quran has stressed over and over again that the Prophet (peace be upon him) is not only a giver of good news to the believers but he is also their teacher, their lawgiver, judge and guide, a purifier of their morals and a model of life for them, and that every word which he utters is law which they have to obey and follow willingly in all walks of life and for all times to come.
71a. For explanation, see (E.N. 70 of Surah Al-Mominoon).