The role of the Prophet as a warner (natheer)

تَبَارَكَ ٱلَّذِى نَزَّلَ ٱلْفُرْقَانَ عَلَىٰ عَبْدِهِۦ لِيَكُونَ لِلْعَـٰلَمِينَ نَذِيرًا

Blessed is He who sent down the Criterion upon His Servant that he may be to the worlds a warner -