It is straight, to warn of violent force direct from Him, and to give the good news to the believers, those who do right actions, that for them there is an excellent reward, (Qur'an, 18:2)
This is a communication to be transmitted to mankind so that they may be warned by it and so that they will know that He is One God and so that people of intelligence will pay heed. (Qur'an, 14:52)
In this way We have sent it down as an Arabic Qur'an and We have made various threats in it so that hopefully they guard against evil or it will spur them into remembrance. (Qur'an, 20:113)
By the Book which makes things clear. We sent it down on a blessed night; We are constantly giving warning. (Qur'an, 44:2-3)