After Allah, the Exalted, mentions that on the Day of Judgement both the good and the evil will be recompensed and there is no avoiding it, He then explains that the Qur'an was revealed as a bringer of glad tidings and a warner in the clear and eloquent Arabic language. There is no confusion or deficiency in it.
﴿وَصَرَّفْنَا فِيهِ مِنَ الْوَعِيدِ لَعَلَّهُمْ يَتَّقُونَ﴾
(And thus We have sent it down as a Qur'an in Arabic, and have explained therein in detail the warnings, in order that they may have Taqwa of,) This means: so that they will leave off sins, forbidden things and lewd abominations.
﴿أَوْ يُحْدِثُ لَهُمْ ذِكْراً﴾
(or that it may cause them to have a lesson from it.) This means: to produce acts of obedience and deeds that will bring one closer to Allah.
﴿فَتَعَـلَى اللَّهُ الْمَلِكُ الْحَقُّ﴾
(Then High above all be Allah, the True King.) This means: Most Holy and Majestic is He, the True King, Who is Himself the Truth and His promise is true. Likewise, His threat is true, His Messengers are true, the Paradise is true, the Hellfire is true and everything from Him is true. His justice is that He does not punish anyone before warning them, sending Messengers to them and granting excuses to His creatures, so that no one will have any argument or doubt (on Judgment Day).