The real work of the Prophet is to be an exponent of the truth (shaahid, as translated by Shah Waliullah). He should clearly show who will be entitled to God’s Grace and who will deserve punishment from God in the eternal life after death.
The rising of such a ‘shaahid’ or witness of Truth poses the greatest trial for his addressees. They have to hear God’s voice in the voice of a human being. They have to see a representative of God in the shape of a human being. While giving their hand into the hands of a man, they have to think that they are giving their hand into the hands of God. For those who prove to have this superior insight, God has great rewards in store, but to those who fail in this test, God will mete out the most severe punishment.