This Ayah chastises the People of the Book for the transgression and prohibitions they committed by their denials in the past and more recent times, of Allah's Ayat and the Messengers. They did this due to their defiance and rejection of the Messengers, denial of the truth and refusal to follow it. They also killed many Prophets when they conveyed to them what Allah legislated for them, without cause or criminal behavior committed by these Prophets, for they only called them to the truth,

وَيَقْتُلُونَ الَّذِينَ يَأْمُرُونَ بِالْقِسْطِ مِنَ النَّاسِ

(And kill those men who order just dealings) thus, demonstrating the worst type of arrogance. Indeed, the Prophet said,

«الْكِبْرُ بَطَرُ الْحَقِّ وَغَمْطُ النَّاس»

(Kibr (arrogance) is refusing the truth and degrading people)

This is why when they rejected the truth and acted arrogantly towards the creation, Allah punished them with humiliation and disgrace in this life, and humiliating torment in the Hereafter. Allah said,

فَبَشِّرْهُمْ بِعَذَابٍ أَلِيمٍ

(then announce to them a painful torment) meaning, painful and humiliating,

أُولَـئِكَ الَّذِينَ حَبِطَتْ أَعْمَـلُهُمْ فِي الدُّنْيَا وَالاٌّخِرَةِ وَمَا لَهُم مِّن نَّـصِرِينَ

(They are those whose works will be lost in this world and in the Hereafter, and they will have no helpers. ).