Ayah

أَعَدَّ ٱللَّهُ لَهُمۡ عَذَابًا شَدِيدًا ۖ فَٱتَّقُواْ ٱللَّهَ يَٰٓأُوْلِى ٱلۡأَلۡبَٰبِ ٱلَّذِينَ ءَامَنُواْ ۚ قَدۡ أَنزَلَ ٱللَّهُ إِلَيۡكُمۡ ذِكۡرًا
Translation

Allah has prepared for them a severe Punishment (in the Hereafter). Therefore fear Allah, O ye men of understanding - who have believed!- for Allah hath indeed sent down to you a Message,-<br/>
Tafsir

God has prepared for them a severe chastisement (the reiteration of the threat is for emphasis). So fear God, O people of pith, O possessors of intellect, [you] who believe! (this is a description of the vocative, or an explication of it) God has certainly revealed to you a [source of] remembrance, that is, Al-Qur'an;