In The Name of Allah, The Most Merciful, The Bestower of Mercy.
وَقَالَ ٱلَّذِينَ كَفَرُوا۟ لَا تَسْمَعُوا۟ لِهَٰذَا ٱلْقُرْءَانِ وَٱلْغَوْا۟ فِيهِ لَعَلَّكُمْ تَغْلِبُونَ
And those who disbelieve say, “Do not listen to this Qur’an and speak noisily during [the recitation of] it that perhaps you will overcome.” [Surah Fussilat. Ayah 26]
Allah [The Exalted] informs us about the manner in which the disbelievers turned away from the Qur’an and enjoined one another to do so. Allah said: [وَقَالَ ٱلَّذِينَ كَفَرُوا۟ لَا تَسْمَعُوا۟ لِهَٰذَا ٱلْقُرْءَانِ – And those who disbelieve say, “Do not listen to this Qur’an]- Meaning, turn away by not lending an ear to it, beware of paying attention, listening to it or to the one who conveys it (i.e. the Prophet). However, if you do hear it, or hear the call to its rulings, then [وَٱلْغَوْا۟ فِيهِ – speak noisily]- Meaning, utter speak that has no benefit (i.e. gibberish), rather, it (should be speech) that is harmful; and as much as you are able, neither allow anyone to speak to you about it nor recite of its words and meanings to you. This was their Lisaan Al-Haal [i.e. their state of affairs with regards to how they acted] and their Lisaan al-Maqaal [i.e. what they uttered with their tongues] with regards to turning away from this Qur’an.
[لَعَلَّكُمْ تَغْلِبُونَ – that perhaps you will overcome]- Meaning, if you do so, you will overcome. This is a testimony from the enemies, while the truth becomes more manifest as its enemies bore witness in its favour. That is because they decided that they could not overcome the one who conveyed it (i.e. the Prophet) unless they turn away and enjoin one another to do so. And that which is understood from their statement is that if they did not speak noisily, but rather they lend an ear and paid attention to it, they would not be able to overcome because the truth always overcomes and cannot be overcome. This is known to those who adhere to the truth and the enemies of the truth.
Then Allah said:
فَلَنُذِيقَنَّ ٱلَّذِينَ كَفَرُوا۟ عَذَابًا شَدِيدًا وَلَنَجْزِيَنَّهُمْ أَسْوَأَ ٱلَّذِى كَانُوا۟ يَعْمَلُونَ
ذَٰلِكَ جَزَآءُ أَعْدَآءِ ٱللَّهِ ٱلنَّارُ لَهُمْ فِيهَا دَارُ ٱلْخُلْدِ جَزَآءًۢ بِمَا كَانُوا۟ بِـَٔايَٰتِنَا يَجْحَدُونَ
But We will surely cause those who disbelieve to taste a severe punishment, and We will surely recompense them for the worst of what they had been doing. That is the recompense of the enemies of Allah: The Fire, therein will be for them the eternal home, a (deserving) recompense for that they used to deny Our Signs. [Surah Fussilat. Ayaat 27-28] (1)
Ref 1: An Excerpt from Tafseer as-Sadi. slightly paraphrased