The Revelation began when it was time for humanity to reach maturity. The Prophet's mission and that of his community was to become the most complete, progressive, and dynamic exemplars for humanity, and to achieve such a level of advancement that they would be the masters and guides for all subsequent people. But these reformers first had to be reformed. Their qualities and characters had been conditioned by the surrounding non-Islamic environment in which their people had been living for centuries. Islam was to turn their good qualities into qualities of unsurpassed excellence, and to purge their bad qualities and habits in such a way that they would never reappear.
If the Qur'an had been revealed all at once, how would they have reacted to its prohibitions and commandments? Certainly, they would have been unable to understand, let alone accept and apply, them in the ideal manner. This lack of gradualism would have been self-defeating, as proven by history: Wherever Islam was taken, it spread gradually but steadily, and so became firmly established.
We see people all around us who cannot free themselves from their bad habits and addictions. If you confined such people, even if you convinced them to abandon their habits for their own benefit, they would not be happy with you. On the contrary, they would feel angry, bored, and irritated. They would complain and try to escape from your program of reform, so that they could revert to their habits as soon as possible. All the arguments and documented evidence of specialists and experts would not persuade them to change. Even those who were cured occasionally suffer a relapse. Indeed, some of those who campaign against such harmful habits as smoking and consuming alcohol still indulge in them!
Remember that the Qur'an came to change not one or two habits; it came to change everything: ways of living and dying, marrying, buying and selling, settling disputes, and how to perceive one's relation with the Creator, among others. Given the scope of the change envisioned, we can begin to grasp why it was revealed in stages.
The gradual revelation of the Qur'an prepared the people to accept and then live the virtues, excellent manners, and lofty aspirations it demanded. That so much was achieved in only 23 years is a miracle. As Said Nursi said: "I wonder if the scholars of today went to the Arabian peninsula, could they accomplish in 100 years even 1 percent of what the Prophet accomplished in 1 year?" Current campaigns to eradicate such a peripheral vice as smoking employ famous scholars, individuals, institutions, and the whole network of mass media—yet they still result in overall failure. If 20 fewer people die on the road per year after a campaign against alcohol, it is considered a great success. What the Prophet accomplished, at God's bidding, over 23 years far surpasses what all of humanity has managed to achieve since that time.
The Qur'an was revealed in stages so that its audience could understand, internalize, and apply its prohibitions, commands, and reforms. Revelation came when the need for guidance arose, without discouraging or grinding down morale: warning and condemnation preceded prohibition, appeal and exhortation preceded command. For instance, alcohol and other intoxicating drinks were prohibited in three or four stages; female infanticide in two stages; uniting warring tribes and building up a close-knit society based on brotherhood, thus raising the collective consciousness, in several stages. These difficult reforms were not gestured at or expressed in slogans—they were achieved.
Today, we design our projects according to past experience and future possibilities. Taking possible social and economic fluctuations into account, we make our plans flexible in order to leave room for any necessary modifications. Just like a young tree, the early Muslims grew slowly, adapting gradually to new conditions and thus developing naturally. Every day new people were coming into Islam. New Muslims were learning many things, gaining in Islamic consciousness, training themselves to act upon Islam, and thus becoming members of a society rather than separate individuals or mutually hostile clans. Their characters and personalities, their whole lives, were reshaped and reordered in accordance with Islamic precepts and the Qur'anic guidance.
Such was the magnitude of their spiritual, moral, intellectual, and even physical regeneration. This transformation was achieved through a balanced synthesis of worldly life and spiritual advancement, and it happened gradually, slowly yet continuously, and harmoniously.