Allah says, if you witnessed the angels capturing the souls of the disbelievers, you would witness a tremendous, terrible, momentous and awful matter,

(they smite their faces and their backs), saying to them,

Ibn Jurayj said that Mujahid said that,

(and their backs), refers to their back sides, as happened on the day of Badr. Ibn Jurayj also reported from Ibn 'Abbas, "When the idolators faced the Muslims [in Badr], the Muslims smote their faces with swords. When they gave flight, the angels smote their rear ends."

Although these Ayat are describing Badr, they are general in the case of every disbeliever. This is why Allah did not make His statement here restrictive to the disbelievers at Badr,

In Surat Al-Qitāl (or Muhammad chapter 47) there is a similar Ayah, as well as in Surat Al-An'am,

(And if you could but see when the wrongdoers are in the agonies of death, while the angels are stretching forth their hands (saying): "Deliver your souls!") [6:93]

The angels stretch their hands and smite the disbelievers by Allah's command, since their souls refuse to leave their bodies, so they are taken out by force. This occurs when the angels give them the news of torment and Allah's anger. There is a Hadith narrated from Al-Bara' that when the angel of death attends the disbeliever at the time of death, he comes to him in a terrifying and disgusting shape, saying, "Get out, O wicked soul, to fierce hot wind, boiling water and a shadow of black smoke." The disbeliever's soul then scatters throughout his body, but the angels retrieve it, just as a needle is retrieved from wet wool. In this case, veins and nerve cells will be still attached to the soul. Allah states here that angels bring news of the torment of the Fire to the disbelievers. Allah said next,

(This is because of that which your hands forwarded.) meaning, this punishment is the recompense of the evil deeds that you have committed in the life of the world. This is your reckoning from Allah for your deeds,

Certainly, Allah does not wrong any of His creatures, for He is the Just, who never puts anything in an inappropriate place. Honored, Glorified, Exalted and Praised be He, the All-Rich, Worthy of all praise. Muslim recorded that Abu Dharr said that the Messenger of Allah ﷺ said;

This is why Allah said,