It is said that best criterion for judging the integrity and sincerity of a reformer is this: What are the changes he had undergone in his personal, social, physical and spiritual life, between the early days of when he began pursuing his cause until he achieved success?
For example, in his early days such a man would be modest and generous, self-sacrificing and humble. In short, in regards to his morals and virtue, he would set an example as a pure and distinguished character. Did he achieve success in his jihad and find a place in the hearts and minds of the people? Did he manage to remain in his previously pure state and act as a role model? Or did his success, as happens with many supposed great men, make him lose his head in the clouds of arrogance and conceit.
This, then, is the clearest mirror that will reflect the true face of the true character and personality of any man with a serious mission, no matter how great or small.
Those who have demonstrated the greatest successes in this difficult test have been firstly the Prophets, foremost the greatest of the Prophets (saw), followed by his companions and successors, then by other great people who have walked on his path of light.
Source: Preface of “Bediuzzaman Said Nursi: The Authorised Biography”