The religion handed down by the Prophet remains one and the same. However, since the situations in human society are subject to change, it becomes essential that the original religion (al-din) could be reapplied to changing sets of circumstances through ijtihad. Ijtihad means reapplying divine injunctions to new situations. For instance, the Shariah permitted the touching of leather socks with wet hands for purification instead of the normal washing of feet during ablution. Now when socks made of artificial fibres came to be used, the question arose as to whether doing masah (rubbing with water) was lawful or not. Then it became necessary to re-apply the old injunction to the new situation; after the exercise of ijtihad, permission was given to do masah on these socks.

In every age, the necessity arises of re-applying divine injunctions. And this has happened in modern times on a large scale. In ancient times war was a means of settling conflicts, but with the invention of the latest deadly weapons, war today serves no positive purpose. Now power lies in peace alone. Such is the state of affairs that the commands of war in Islam require a reapplication. In days gone by, kingship, whereby the ruler unilaterally possessed absolute power, was the order of the day. Now it is the age of democracy, which is another name for the politics of power-sharing.

Changed situations in every age demand that efforts be made towards adaptation of the injunctions of Islam to meet new exigencies. This is the way that the Islamic Shariah continues to be updated. This task of updating is performed through ijtihad, a process which, in any community, requires creative thinking. And the essential condition for creative thinking lies in people having full freedom of expression, including that of criticism. This is why Islam has accorded such freedom to everyone, it is in an atmosphere in which everything and everyone is open to criticism that creativity is developed. Creative minds alone can perform the task of ijtihad at the highest level. Where there is no such open intellectual atmosphere, the process of mental development will come to a halt, and that of updating as well.

Source: Islam Rediscovered