According to the dictionary, نَسْخ means to efface and to dispel while, in the terminology of the Shari'ah, it means altering one ruling and replacing it with another one. For example:
After the emigration to Medinah, the Muslims, for a period of fifteen months, offered their prayers in the direction of Bayt al-Maqdas after which the order to change the Qiblah was issued and all of them were obliged to face the Ka'bah while offering their prayers.
In verse 15 of Suratul Nisa, the punishment stipulated for women, who committed fornication, was that if four witnesses testified to the crime they should be imprisoned in the house until death overtook them or until the time Allah (s.w.t.) decreed another alternative for them.
This verse was abrogated by means of verse 2 of Suratul Nur in which their punishment was changed to one hundred lashes.
At this juncture, there is a well-known objection, which is propounded as follows: If the first ruling possessed expediency and common good, then why was it abrogated? And if not, why was it legislated in the first place?
In other words: Why was this ruling not legislated from the very beginning so as to not have needed alteration?
Islamic scholars, since ancient times, have presented the answer to this question in their books which, together with our explanation, is as follows:
We do know that at times, with the change in time and conditions of the environment, man's needs change while at other times they remain stable. One day a programme guarantees his success while on another day, due to changes in circumstances, it is likely that the same programme acts as an obstacle in his path of progress.
One day a particular medicine is extraordinarily effective for a sick person and so the doctor prescribes it for him, but on another day, due to a comparative betterment of his state, it is possible that this medicine could even be detrimental for him and so the doctor orders it to be discontinued and substitutes it with another medicine.
It is possible that a book is beneficial for a student this year but useless for him the next. An experienced teacher should adjust the course such that year after year only those books, which are necessary for the students and ought to be taught.
This issue, especially in view of the laws regarding the development of man and societies, becomes clearer; in the course of human development and perfection, at times a programme is beneficial and constructive while at times, detrimental and therefore in need of a change. The need for changing the curriculum at various time-intervals appears to become more manifest, particularly during the start of social and ideological revolutions.
Of course, it ought not to be forgotten that the fundamentals of Divine laws which constitute the basic foundations are the same everywhere; under no circumstances shall Unity, social justice or hundreds of other such rulings ever undergo an alteration. The change only occurs in secondary issues.
Additionally, it should not be forgotten that indeed the development of religions can reach such a state that the final religion is revealed as the Seal of the religions, such that there can be no alteration in its rulings.1