And We have placed over their hearts coverings, lest they understand it, and in their ears deafness. And when you mention your Lord alone in the Qur’ān, they turn back in aversion.
Allah says to His Messenger Muhammad : `When you recite Qur'an to these idolators, We put an invisible veil between you and them.' Qatadah and Ibn Zayd said, "It is coverings over their hearts," as Allah says:
(And they say: "Our hearts are under coverings (screened) from that to which you invite us; and in our ears is deafness, and between us and you is a screen) meaning, there is something that is stopping and preventing your words from reaching us.
حِجَابًا مَّسْتُورًا
(an invisible veil.) meaning something which covers, or that cannot be seen, so there is a barrier between them and guidance. This is the interpretation that Ibn Jarir (may Allah have mercy on him) thought was correct. Al-Hafiz Abu Ya`la Al-Mawusili recorded that Asma' bint Abi Bakr (may Allah be pleased with her) said, "When the Ayah,
The meaning of Tasbih (glorification of Allah) said by the heavens and the earth and everything present therein
Among these, the Tasbih of Allah said by all angels and believing jinn and human beings is self-evident. Everyone knows that. As for disbelieving human beings and the jinn, they obviously do not say it. Similarly, there are other things in this universe about which it is said that they are insensate, devoid of reason and intelligence. How do we rationalize their act of saying Tasbih? Some ` Ulama' say that their Tasbih is circumstantial, state-articulated, the testimony of their state of being - because, the collective condition of everything other than Allah Ta’ ala is telling us that it is neither permanent existence-wise nor survival-wise. This whole ongoing condition has been activated under the power and control of some supreme power - this testimony is its Tasbih.
When the Quran is recited to people, they fail to understand the message due to their deep conditioning. In fact, they are so frivolous about the world hereafter, that they ignore the message altogether. People are so involved in their worldly matters that truth is no longer their concern. Their reluctance is due to the fact that they do not want to revise themselves. The call of pristine truth always negates their worldly concerns. That is why they are greatly provoked on hearing this call. In their hearts they do not believe in the accountability of the Day of Judgement and this makes them non-serious in their approach to it. The mind which lacks seriousness is incapable of understanding anything of value.
Uthmani text of the Madinah mushaf (King Fahd Complex). Translation: Saheeh International. Tafsir via Quran.com.