فَإِنَّما يَسَّرناهُ بِلِسانِكَ لِتُبَشِّرَ بِهِ المُتَّقينَ وَتُنذِرَ بِهِ قَومًا لُدًّا

So, [O Muhammad], We have only made Qur'an easy in the Arabic language that you may give good tidings thereby to the righteous and warn thereby a hostile people.