"They will say," meaning: the devils to the polytheists among mankind, "Rather, you yourselves were not believers."
﴿قَالُوا﴾ يَعْنِي: الشَّيَاطِين للْمُشْرِكين من الْإِنْس ﴿بَل لَّمْ تَكُونُوا مُؤْمِنِينَ﴾.