What is The Divine Wisdom in The Qur'an's being revealed in stages over a period of 23 years?

From: http://www.islamanswers.net/Quran/stages.htm

What is The Divine Wisdom in The Qur'an's being revealed in stages over a period of 23 years?
The Qur’an was revealed in stages over a period of 23 years, and not as a complete book in one single act of revelation. There is wisdom and a number of reasons for this, which we shall try to explain, inshaAllah. However, before doing so, let us note that had the Qur’an not been revealed in this way but, instead, all at once, then those who ask this question would certainly have asked, ‘Why was it sent down as a complete book in one single act of revelation but not in stages over time?’ What is essential in all matters of religion is a sufficient humility and obedience in our attitudes, precisely so that we may understand and come to benefit from Divine decrees and commandments. Otherwise, questions of a similar kind can be asked endlessly and, of course, fruitlessly: for example, why is the midday prayer in so many units while the congregational prayer on Friday is a different number? Why is the rate of zakat 2.5 per cent and not 2? The weight and the duration of particular prayers, the rate of the zakat and other matters of this kind are decreed by God, the All-Wise and All-Knowing. When we determine any matter, it is always from a limited viewpoint: by our very nature as created beings our reasoning is partial, inadequate: we barely understand what is in front of our noses and when we make choices we do so with our own immediate condition in mind─our present capabilities, our daily routines, our style and standard of living, and so on. By contrast, the Divine Decree takes everything into account─our moral and spiritual well-being as well as our worldly happiness, our future as well as our present─and weaves the whole into a single pattern, coherent with Grace and Wisdom. Because of this, the benefit that man derives from the Divine commandments is immeasurable, the blessings that flow from obedience to them is beyond our imagination.
That principle applies to the revelation of the Qur’an in stages over years. The essence of servanthood to God is to submit to and implement the Divine commandments in one’s life; if we discuss this matter it is only with the clear aim of seeking to understand the wisdom in its being so and not otherwise. By no means is it our purpose to somehow question the Divine Reasoning.
The time at which the Qur’an began to be revealed was the time for humanity to come to maturity. That is why, Muhammad, upon him be peace, the perfect model for humanity, the best example to be studied and followed, for whose sake indeed the universe was created, was given his mission at that time. His mission and the mission for the umma (the society of Muslims) that gathered around him was to become the most complete, progressive and dynamic exemplars for mankind: to attain to the top rung of human advancement and be the masters and guides for all civilized people thereafter. But these reformers to be had first to be themselves reformed. Their qualities and characters were deeply conditioned by the ways in which they had long been accustomed to living. Islam was to turn their good qualities into qualities of unsurpassed excellence, but Islam had also to get rid of their bad qualities and bad habits. To eradicate their vices, to replace them with virtues and the highest moral aspiration, in a way such that the change would be secure for all time─this was one of the purposes of the Revelation. If the Qur’an had been given in one single act of revelation, if it had stood on their way with all its prohibitions and commandments, they could never have understood, let alone accepted and applied, them in the ideal manner. In fact, such a way would be contrary to the course that mankind were to adopt so as to gradually implement the laws of God and thus evolve: ever since then, in every part of the world where Islam has been taken, it has spread gradually but steadily and rooted deeply.
We can see nowadays people all around unable to free themselves from their bad habits and addictions, such as idling in front of shop windows (mistakenly considered to be harmless), smoking, drinking and taking other addictive drugs. If you confined such people, even if you convinced them completely of the negative consequences of their habits, and the benefit of giving them up, they would not be happy with you, rather the contrary: they would feel angry, bored, irritated and begin to complain; they would seek escape from your program of reform and revert to their habits as soon as they were free to do so. All the arguments, all the evidence of specialists and experts of all kinds, medical or sociological, proving beyond doubt the physical, mental and social harm caused by such addictions, would fail to persuade them to change their lifestyle. Even people cured of the chemical effects of such addictions still lapse back into them, even though what they revert to is not one of the essentials of life. Indeed, there are cases of people who have campaigned against harmful habits like smoking and drinking but cannot themselves quit their own indulgence in those habits. If we bear this in mind, and remember too that we are not speaking of the reform of one or two individual bad habits but of the reform of a whole lifestyle, of ways of living and dying, of marrying, of buying and selling, of settling disputes, above all, a way of thinking about man’s relation with his Creator─then we begin to grasp why the Qur’an was revealed in stages.
The revelation of the Qur’an hoed out the weeds in people’s hearts, rid them of pests and other nuisances, and so made them a good soil for the cultivation of the virtues, excellent manners, and lofty aspirations. That so much was achieved in only 23 years appears to us what it was: a miracle. Bediuzzaman said, ‘I wonder if the scholars of today went to the Arabian Peninsula, would they in a hundred years manage to implement even one percent of what the Prophet Muhammad, upon him be peace, did in a year?’ Today we see that even when many prestigious scholars and institutions and the whole network of the mass media campaign to eliminate so peripheral a vice as smoking, they fail to do so: indeed, if after such a campaign against, say drinking, there are twenty fewer deaths on the roads in a year, they consider it a great success! No alas! The miracle of the Qur’an was unique. Another such is impossible. Mankind has not made so much progress over fifteen hundred years as it did over the period 23 years of the prophethood of Muhammad, peace be upon him and the blessings of God.
That period of 23 years was necessary for those who lived at that time to understand, interiorize and apply the Revelation easily. The Qur’an instituted a great deal of change, through prohibitions and commands and through new reforms of the deepest consequence. However, it established all of them in stages over time, as the need for guidance arose, without discouraging, or grinding down morale: warning and condemnation preceded prohibition; appeal and exhortation preceded command. For instance, intoxicating drinks were prohibited in three or four stages; burying girls alive in two stages; uniting warring tribes, and building up a close-knit society based on brotherhood and thus raising the collective consciousness in a couple of stages. These difficult reforms were not gestured at or expressed in slogans─they were achieved. The believers needed this period to reform and so become reformers.
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, and try to leave room for probably necessary modifications of detail. Just like a young tree, the Muslims in the early days of Islam grew slowly, adapting to new conditions gradually and thus developing naturally. Every day new people were coming into Islam, and the new Muslims were every day learning quite new and different things, gaining in Islamic consciousness, training themselves to act upon Islam and thus become members of a society rather than being separate individuals and clans in a state of war. Their individual characters and personalities, their whole lives, were re-shaped and re-ordered totally in accordance with the precepts of Islam and the Qur’anic guidance. Such was the magnitude of their spiritual, moral, intellectual and even physical regeneration. It was achieved through a balanced synthesis between worldly life and spiritual advancement, and it happened slowly, continuously and harmoniously, in stages over time.
If the Qur’an had been sent down in a single act of revelation, those Bedouins and unsophisticated people could not have borne it. If a person used to living under one atmosphere pressure is suddenly taken to very high altitudes, he dies as a result of the sudden change. Aeroplanes rise gradually to such altitudes, and people use oxygen masks in them. In a similar way, the changes intended by the Qur’an came to a people among whom the Qur’anic values of individual, family and social life, of iman (conviction) and din (religion) meant little. Now, if the Qur’an had stood on their way with all its reforms, and asked the people to implement them fully, no one would have understood, let alone accepted, it. That would be like taking them to high altitudes in a few seconds and causing their death. That is why, the ordinances of the Qur’an were sent to and inculcated in people in stages, out of consideration for what best fits human nature.
Since man is a part of the universe, we cannot consider him out of the context of the laws governing the universe. Just as everything in the universe develops and progresses in stages, so too man’s progress and development is most fittingly and enduringly secured in stages. The Qur’an is the basis and foundation of that progress and development, and had therefore to be revealed, in accordance with the Divine Wisdom which comprehends all things, in stages over 23 years. And yet, that it was 23 and nor 22 or 24, we do not presume to question: rather, whatever it had been, we would accept humbly and in full submission. Praise be to God, the Lord of the worlds, and peace and the blessings of God on Muhammad, His Prophet and Messenger.