"And when your Lord declared" - al-Hasan said: meaning, your Lord made it known, "that He would surely continue to send against them until the Day of Resurrection those who would afflict them with" - meaning, those who would impose upon them, "the worst torment" - meaning, its severity.
Qatadah said: So He sent the Arabs against them, and they are, because of this, in torment through the jizyah (poll tax) and humiliation.
"Indeed, your Lord is swift in penalty" - al-Hasan said: When Allah intends to punish a people, His punishment of them is swifter than the blink of an eye.
"And indeed, He is Forgiving, Merciful" - to those who repent and believe.
﴿وَإِذ تَأذن رَبك﴾ قَالَ الْحَسَنُ: يَعْنِي: أَعْلَمَ رَبُّكَ ﴿لَيَبْعَثَنَّ عَلَيْهِمْ إِلَى يَوْمِ الْقِيَامَةِ من يسومهم﴾ أَي: يوليهم ﴿سوء الْعَذَاب﴾ أَيْ: شِدَّتُهُ.
قَالَ قَتَادَةُ: فَبَعَثَ عَلَيْهِم الْعَرَب، فهم مِنْهُ فِي عذابٍ بِالْجِزْيَةِ وَالذُّلِّ.
﴿إِنَّ رَبك لسريع الْعقَاب﴾ قَالَ الْحَسَنُ: إِذَا أَرَادَ اللَّهُ أَنْ يُعَذِّبَ قَوْمًا كَانَ عَذَابُهُ إِيَّاهُمْ أَسْرَعَ مِنَ الطَّرْفِ.
﴿وَإِنَّهُ لغَفُور رَحِيم﴾ لمن تَابَ وآمن.
