Before the advent of Islam, they put a higher value on the blood of a member of their own clan and demanded the life of a man of the same rank from the clan of the murderer or the lives of scores or even hundreds from the tribe of the murderer according to the value put on the blood of the slain. On the other hand, if the murderer happened to belong to a higher rank than that of the slain, their "judgement" was that the life of the murderer should not be taken for the life of the slain. And this inequality in the evaluation of blood was not confined only to that age of ignorance. Even today the "civilised" nations are not ashamed of declaring openly that if one person of their nation is killed, they will take the lives of fifty men from the nation of the murderer. And they put these challenges into practice. We often hear that so many people belonging to the subject nation have been put to death to avenge the murder of one person belonging to the ruling nation. But if the murderer belonged to a "civilised" ruling nation and the slain to an "uncivilised" subject nation, their judges would not pass the sentence of death on him. In order to guard against these unjust rules, Allah has ordained that the life of the murderer and the murderer alone should be taken for the life of the slain, irrespective of the rank or race of the murderer or that of the slain.  

Desc No: 178
The use of the word "brother" here contains a kind of recommendation. That is, "Though the murderer has injured you very grievously, he is after all your brother by the human relation. Therefore, if you restrain your rage against your erring brother and refrain from retaliation and remit the penalty of death, you will raise your standard of humanity."

This verse also shows that, according to the lslamic Penal Code, even murder is a compoundable offence. The heirs of the murdered person have the right to pardon the murderer, if they deem it proper. In that case the court cannot insist on taking his life. Of course, the murderer will have to pay the blood money if the rightful claimants demand it.  

Desc No: 179
The word "ma'ruf" has been used in many places in the Qur'an. It refers to those just and rational rules of conduct which are generally known and accepted by all fair-minded people. They are so clear and well known that everyone who is not blinded by self-interest and prejudice will acknowledge them as right and just, and the Islamic law recognizes them in all those matters for which it has not laid down any regulations. Such common laws and general usages are termed "ma ruf . 

Desc No: 180
For instance, it will be transgression if the heirs of the slain try to retaliate even after accepting the ransom, or if the murderer does not mean to pay the ransom gracefully, or otherwise reacts in an ungrateful manner.  

Desc No: 181
This verse refutes the opinion of those people who go to the other extreme and advocate total abolition of capital punishment. If it is inhuman to insist on retaliation, it is equally inhuman to encourage murder by totally abolishing capital punishment, as has been done in some "civilised" countries. That is why Allah declares that there is life for society in the law of retribution. If a society does not pay due regard to the sanctity of life and tries to protect a murderer, it sets a premium on crime and puts in danger the lives of many innocent people.  "