"And among them are those who listen to you, but We have placed coverings over their hearts, lest they understand it," meaning: so that they would not understand it. "And in their ears is deafness," meaning: deafness to the guidance.
"And if they see every sign," meaning: what they requested from the Prophet (may Allah bless him and grant him peace) in terms of signs.
"They will not believe in it, until, when they come to you arguing with you," and their argument is that "those who disbelieve say, 'This is not but legends of the former peoples,'" the lies and falsehoods of the ancients; they mean: the Quran.
﴿وَمِنْهُمْ مَنْ يَسْتَمِعُ إِلَيْكَ وَجَعَلْنَا عَلَى قُلُوبِهِمْ أَكِنَّةً أَنْ يَفْقَهُوهُ﴾ لِئَلَّا يَفْقَهُوهُ. ﴿وَفِي آذَانِهِمْ وَقْرًا﴾ يَعْنِي: صَمَمًا عَنِ الْهُدَى.
﴿وَإِنْ يرَوا كل آيَة﴾ يَعْنِي: مَا سَأَلُوا النَّبي ﷺ مِنَ الْآيَاتِ.
﴿لَا يُؤْمِنُوا بِهَا حَتَّى إِذا جاءوك يجادلونك﴾ وَمُجَادَلَتُهُمْ أَنْ ﴿يَقُولُ الَّذِينَ كَفَرُوا إِنْ هَذَا إِلا أَسَاطِيرُ الأَوَّلِينَ﴾ كَذِبُ الْأَوَّلِينَ وَبَاطِلُهُمْ؛ يَعْنُونَ: الْقُرْآنَ.