Why do you consider this necessarily to be so? The role of a prophet in the OT and contemporaneously is much more complicated than a simple prognosticator. *First a prophet was one who saw or watches (Isa 29:10;43:10-12;Eze.33:7). *Secondly, he would be a witness or martyr to that which he saw. He would promote the saving ordinances of the gospel, the decrees and rites. (Isa I1:11-12(but)1:13 and DC 132:2-4). He would keep the scripture alive in the hearts of the new generation.(Isa 50:4;DC 68:4) He would teach that Israel had been elected by God and had a special covenant with him. He would teach them a sense of belonging that Israel was a place set apart. That Israel alone taught about the real God. (Isa. 40:11;DC49:9,36) *He would also render Gods judgement (Isa 30:12-14;Jer. 5:3,12,14;DC 19:3, God's compassion or mercy which implied a covenant. (Isa 54;7-8 ;DC 64:2;101:9), redemption (Isa 51:11;DC29:42), and final consummation (Isa 53:4-5/2:2-4) *Finally he would seal his life with his death.