"And they used to persist"—meaning, they persisted "in the great sin," which is shirk (polytheism).
﴿وَكَانُوا يصرون﴾ يُقِيمُونَ ﴿على الْحِنْث﴾ يَعْنِي: الذَّنب ﴿الْعَظِيم﴾ وَهُوَ الشّرك
