God sends a "Mujaddid"
The Arabic word mujaddid means someone who "revives and renovates the religion." In his hadiths, our Prophet (may God bless him and grant him peace) states that at the beginning of every century, God sends a blessed person from his lineage to explain the facts of the religion according to the necessities of the time.
God will raise for this community at the end of every hundred years the one who will renovate its religion for it. (Sunan Abu Dawud)
On this issue, the great Islamic scholar Imam Rabbani states the following:
At the head of each century, God sends a mujaddid among the ulama of this community who revives the Shariah [the essence of Qur'anic moral values and the Sunnah of our Prophet (saas)]. (Imam Rabbani)
About the same subject, Bediuzzaman said:
"In every century, God sends a mujaddid." (Bediuzzaman Said Nursi, Risale-i Nur Collection, Barla Letters, 119)
Bediuzzaman states that the mujaddid of the twelfth century was Mevlana Halid. (Barla Letters, 120)
In the fourteenth Islamic century, the Risale-i Nur (Bediuzzaman's collected works) served this purpose, as follows:
"Exactly after a century, the cures of the Risale-i Nur appear all around and serve to the very same purpose... With the meaning fortified by the clear expression of the hadith, it is our conviction that, in terms of reviving the religion, the Risale-i Nur is in the position of a mujaddid." (Barla Letters, 121)
Bediuzzaman gives the good news that the mujaddid of the fifteenth century will be the Mahdi:
"Now most of the situations among the Muslims that are opposed to the light of the Qur'an are the grave outcomes of those evil intents and the cruel covenants such as the Treaty of Sèvres. If the letter "mim" bearing the gemination mark is counted as one, like the letter "lam" bearing the gemination mark, it would be 1284 [Hijri]. The European unbelievers who aimed to extinguish the light of the State of Islam at that time provoked the Russians ten years later and curtained the bright light of the Islamic world with a temporary cloud by means of the Russia's gloomy War of 93 [1877-1878 The Ottoman-Russian War]. However, since these oppressions of cloud were dissolved by the disciples of Mevlana Halid-i Bagdadi and not by the disciples of Risale-i Nur, from this point of view this verse symbolically points to them.
It now occurs to mind that if each of the letters "mim" and "lam" bearing the gemination mark are counted as two, the people who will dissolve the oppressions a century later may be the disciples of the Mahdi." (Bediuzzaman, Risale-i Nur Collection, First Ray, p. 85)
As this explanation reveals, Bediuzzaman states that the cruelty found within the Islamic world can be removed only "one century later" by the Mahdi. He explained that during the fifteenth Islamic century, the works of the Mahdi will save people from great trouble and make them attain deliverance.