Tafsir Ibn Kathir -> Surah Al-Anfal -> Allah commands the Angels to fight and support the Believers

Allah said next,

﴿إِذْ يُوحِى رَبُّكَ إِلَى الْمَلَـئِكَةِ أَنِّي مَعَكُمْ فَثَبِّتُواْ الَّذِينَ ءَامَنُواْ﴾

((Remember) when your Lord revealed to the angels, "Verily, I am with you, so keep firm those who have believed.'')

This is a hidden favor that Allah has made known to the believers, so that they thank Him and are grateful to Him for it. Allah, glorified, exalted, blessed and praised be He, has revealed to the angels -- whom He sent to support His Prophet, religion and believing group -- to make the believers firmer. Allah's statement,

﴿سَأُلْقِى فِي قُلُوبِ الَّذِينَ كَفَرُواْ الرُّعْبَ﴾

(I will cast terror into the hearts of those who have disbelieved.) means, `you -- angels -- support the believers, strengthen their (battle) front against their enemies, thus, implementing My command to you. I will cast fear, disgrace and humiliation over those who defied My command and denied My Messenger, f

﴿فَاضْرِبُواْ فَوْقَ الأَعْنَـقِ وَاضْرِبُواْ مِنْهُمْ كُلَّ بَنَانٍ﴾

(so strike them over the necks, and smite over all their fingers and toes.) strike them on their foreheads to tear them apart and over the necks to cut them off, and cut off their limbs, hands and feet. It was said that,

﴿فَوْقَ الأَعْنَـقِ﴾

(over the necks) refers to striking the forehead, or the neck, according to Ad-Dahhak and `Atiyyah Al-`Awfi. In support of the latter, Allah commanded the believers,

﴿فَإِذَا لَقِيتُمُ الَّذِينَ كَفَرُواْ فَضَرْبَ الرِّقَابِ حَتَّى إِذَآ أَثْخَنتُمُوهُمْ فَشُدُّواْ الْوَثَاقَ﴾

(So, when you meet (in fight Jihad in Allah's cause) those who disbelieve, smite (their) necks till when you have killed and wounded many of them, then bind a bond firmly (on them, take them as captives).) ﴿47:4﴾

Ar-Rabi` bin Anas said, "In the aftermath of Badr, the people used to recognize whomever the angels killed from those whom they killed, by the wounds over their necks, fingers and toes, because those parts had a mark as if they were branded by fire.'' Allah said,

﴿وَاضْرِبُواْ مِنْهُمْ كُلَّ بَنَانٍ﴾

(and smite over all their fingers and toes.)

Ibn Jarir commented that this Ayah commands, "O believers! Strike every limb and finger on the hands and feet of your (disbelieving) enemies.'' Al-`Awfi reported, that Ibn `Abbas said about the battle of Badr that Abu Jahl said, "Do not kill them (the Muslims), but capture them so that you make known to them what they did, their ridiculing your religion and shunning Al-Lat and Al-`Uzza (two idols).'' Allah than sent down to the angels,

﴿أَنِّي مَعَكُمْ فَثَبِّتُواْ الَّذِينَ ءَامَنُواْ سَأُلْقِى فِي قُلُوبِ الَّذِينَ كَفَرُواْ الرُّعْبَ فَاضْرِبُواْ فَوْقَ الأَعْنَـقِ وَاضْرِبُواْ مِنْهُمْ كُلَّ بَنَانٍ﴾

(Verily, I am with you, so keep firm those who have believed. I will cast terror into the hearts of those who have disbelieved, so strike them over the necks, and smite over all their fingers and toes.)

In that battle, Abu Jahl (may Allah curse him) was killed along with sixty-nine men. `Uqbah bin Abu Mua`it was captured and then killed, thus bring the death toll of the pagans to seventy,

﴿ذَلِكَ بِأَنَّهُمْ شَآقُّواْ اللَّهَ وَرَسُولَهُ﴾

(This is because they defied and disobeyed Allah and His Messenger.) joining the camp that defied Allah and His Messenger not including themselves in the camp of Allah's Law and faith in Him. Allah said,

﴿وَمَن يُشَاقِقِ اللَّهَ وَرَسُولَهُ فَإِنَّ اللَّهَ شَدِيدُ الْعِقَابِ﴾

(And whoever defies and disobeys Allah and His Messenger, then verily, Allah is severe in punishment.) for He will crush whoever defies and disobeys Him. Nothing ever escapes Allah's grasp nor can anything ever stand against His anger. Blessed and exalted He is, there is no true deity or Lord except Him.

﴿ذَلِكُمْ فَذُوقُوهُ وَأَنَّ لِلْكَـفِرِينَ عَذَابَ النَّارِ ﴾

(This is (the torment), so taste it; and surely, for the disbelievers is the torment of the Fire.)

This Ayah addresses the disbeliever, saying, taste this torment and punishment in this life and know that the torment of the Fire in the Hereafter is for the disbelievers.

﴿يَـأَيُّهَا الَّذِينَ ءَامَنُواْ إِذَا لَقِيتُمُ الَّذِينَ كَفَرُواْ زَحْفاً فَلاَ تُوَلُّوهُمُ الأَدْبَارَ - وَمَن يُوَلِّهِمْ يَوْمَئِذٍ دُبُرَهُ إِلاَّ مُتَحَرِّفاً لِّقِتَالٍ أَوْ مُتَحَيِّزاً إِلَى فِئَةٍ فَقَدْ بَآءَ بِغَضَبٍ مِّنَ اللَّهِ وَمَأْوَاهُ جَهَنَّمُ وَبِئْسَ الْمَصِيرُ ﴾

(15. O you who believe! When you meet those who disbelieve, in a battlefield, never turn your backs to them.) (16. And whoever turns his back to them on such a day -- unless it be a stratagem of war, or to retreat to a troop (of his own) -- he indeed has drawn upon himself wrath from Allah. And his abode is Hell, and worst indeed is that destination!)