The Arabic term Naskh implies setting aside, copying and the like. By Naskh is also meant the transcribing of a book and the moving aside of the sunlight by the shade. Technically, however, Naskh implies the abrogation of one religious law by another. The abrogated law is then called Mansukh and the law that replaces it is known as Nasikh.
In contradiction from the other animals man continues to grow intellectually, mentally and culturally with the passage of time. His surroundings and environment, too, continue to change. In all probability then, the moral laws which he must accept would also change with his environment.
The moral laws of the first family of humans is a case in point. There it was morally correct for brothers and sisters to be committed in marriage with each other. For the continuation of the human species such a moral code was indispensable. However, the conditions changed as time went by. Numerous families came into being. Then the law that brothers and sisters were not to marry each other came into effect. It was at a particular stage of the development of the human species that this law came into force. With the revelation of this law, that which was permitted previously was now prohibited. The new law thus became the very cornerstone of the institution of the family and, thereby, of the very existence of human society.
The old law had been given unto the children of Adam by the Lord Creator Himself. The new law, too, had been given by Him. For it is, indeed, He who is best aware of the intricacies of human society. Who besides He Himself can alter the laws required by humanity as the society evolved with time ?
There are various examples from the religious scriptures that show how amendments were made in the laws. Such amendments might have been intended for a particular region or society. It may also have been a wholly general amendment as well.
For instance, consider the ruling concerning the issue of divorce. It is clear from the Old Testament of the Bible (Deuteronomy 24:1-4, Jeremiah 3:12) that divorce had been very common among the Israelites. Jesus had to face a society wherein the permission for divorce was misused and in which the women were, thereby, put to undue hardships. It is now known that in the laws that were revealed to Jesus, there were legislations that sought to strictly curtail the very provision of divorce. The varying manner in which Jesus made his extreme statments against divorce notwithstanding, they have all been quoted faithfully in the collection of the gospels. This ruling against divorce was revealed, perhaps, to bring down the rate of divorce among the Israelites and to restrict that freedom considerably. Jesus himself had made it clear that his mission was confined to the Israelites alone (See Mathew 5:17, 10:5, 15:24). This would then imply that the strict ruling which had prohibited, albeit, in a temporary way, the procedure of divorce, revealed as it was through Jesus Christ, had sought to change the condition of the Israelites whereby the institution of divorce was employed with reckless impunity.
It was the permission for divorce which was, in fact, conceded by the ruling in the Old Testament that was now abrogated by the ruling issued through Jesus. Similarly, many of the rulings in the Old Testament can be seen to have undergone abrogation by other rulings within the Old Testament itself.
In similar fashion, too, many of the rulings in the ancient religious scriptures have been abrogated by the Qur'an. Indeed, some of the earlier rulings in the Qur'an itself have been abrogated by the rulings that were revealed at a later date. Factually, of course, such changes were an indispensable necessity in the due course of societal transformation.