This can be described as loss of interest and is considered to be similar to actions such as mockery, plotting and the likes, which are actions that Allāḥ does in response to what occurs from His servants. Thus, the meaning is that Allāh does not lose interest in rewarding the servant until the servant loses interest in doing righteous deeds. Some scholars said this means that no matter how much you act, Allāh will continue to reward you and does not tire in doing so.
انظر صفة : (الملل).
المصدر: كتاب "صِفَاتُ اللهِ عَزَّ وَ جَلَّ الْوَارِدَةُ فِي الْكِتَابِ وَ السُّنَّة"ِ