Overall meaning :
Allah Almighty declares that it is not lawful for a believer to kill a fellow believer unless this happens unintentionally or accidentally. In the case of accidental killing, the offender must atone for such offence by freeing a believing male or female slave, and blood money becomes due, in which case it is paid on his behalf by his paternal relatives to the victim’s relatives unless they remit it as charity. If the victim, while himself a believer, belongs to a people who are at war with the believers, the offender is only required to free a believing male or female slave; and if the victim belongs to a non-Muslim people with whom the believers are bound by a covenant, then blood money becomes due, in which case it is paid on the offender’s behalf by his paternal relatives to the victim’s relatives and he has, addition, to free a believing male or female slave. Whoever has no means to make such expiation or cannot find a slave to set free must fast two consecutive months—a penance enjoined by Allah to forgive His servants and have mercy on them. Allah is All-Knowing, All-Wise.
Next, He sternly warns against killing a believer, stating that whoever deliberately kills another believer, his punishment in the hereafter is Hell, to abide there for a very long time; Allah will also be angry with him, will exclude him from His mercy and will prepare for him a terrible punishment. Such will be his punishment if Allah inflicts punishment on him.
Then, addressing the believers, He instructs them saying that when they go forth to fight in His cause, they should show discernment and not kill anyone if they are not sure if he is a Muslim or an unbeliever, nor should they say to anyone who surrenders himself to them and offers them the greeting of peace—thereby indicating his being a Muslim—that he is not a Muslim. Rather, they should consider him as he says he is and not kill him, thereby seeking the fleeting gains of the present, worldly life by seizing his possessions as booty, for with Allah there are abundant gains that are far better than such possessions. He reminds them that they, too, used to conceal their faith from their unbelieving people until He bestowed His grace upon them by supporting His religion, thus enabling them to openly profess their faith; therefore, they should not hasten to kill anyone whose religious convictions are not clear, pointing out that He is fully aware of all that they do.