وَقَالُوا قُلُوبُنَا غُلْفٌ ۚ بَل لَّعَنَهُمُ اللَّهُ بِكُفْرِهِمْ فَقَلِيلًا مَّا يُؤْمِنُونَ
Wa qaaloo quloobunaa ghulf; bal la'anahumul laahu bikufrihim faqaleelan maa yu'minoon
And they said, "Our hearts are wrapped shut." Rather, God has cursed them for their denial, so little do they believe.
Ghulf carries two readings that the early reciters transmitted side by side: hearts wrapped in a covering, or hearts that are vessels already full and holding all the knowledge they need. The first is an excuse and the second is a boast, and the reply given fits either. Little is the measure the verse ends on, which concedes that some do believe.