﴿ كِتَٰبٌۭ فُصِّلَتْ ءَايَٰتُهُۥ قُرْءَانًا عَرَبِيًّۭا لِّقَوْمٍۢ يَعْلَمُونَ ﴾

“a divine writ, the messages whereof have been clearly spelled out as a discourse in the Arabic tongue for people of [innate] knowl­edge,”

And after stating these qualities, it is said towards the end of the verse-3, لِّقَوْمٍ يَعْلَمُونَ (for a people who understand) which means that the verses of the Holy Qur'an being in Arabic, their being clear and evident and their communicating good news as well as warnings can only benefit those people who intend to ponder over them and understand them. But the Arabs and the Quraysh, despite all this, turned away from the Qur'an, and let alone trying to understand, they did not even bear to listen to the Qur'an. This has been mentioned at the end of verse 4: "Yet most of them turned away, so they do not listen."