The Qur'aan came to change the beliefs, behaviour and outlook of all who are astray. It came to guide them to true happiness and the way of life that one should follow in this life. Allaah سبحانه و تعالى states,
"O you who have believed! Respond to Allaah and His Messenger as they call you to that which gives you life." (Sooratul-Anfaal, 8:24)
Imaam as-Suddi رحمه الله, an early commentator on the Qur'aan, stated that this verse means that Islaam gave the noble Companions رضي الله عنهم true life after they were truly dead in disbelief. 
The difference between faith and disbelief is truly comparable to the difference between life and death. Knowing the Qur'aan, that source of life to which Allaah and His Messenger is calling every human, as opposed to not knowing it is also comparable to the difference between life and death.
The effect of the Qur'aan can clearly be seen in the first generation of Muslims رضي الله عنهم. These were the people who were given life by the Qur'aan. They were taken from darkness into light. The example these noble people set is the example that all later generations who believe in the Qur'aan must aspire to.
The World Before the Advent of the Prophet Muhammad (صلى الله عليه وسلم)
Shaykh Abul Hasan 'Ali Nadwi رحمه الله, in his work Islam and the World, has done an admirable job of describing the situation of the world before the coming of the time of the Prophet (may Allaah exalt his mention and grant him peace). 
Shaykh Abul Hasan 'Ali Nadwi رحمه الله described the plight of all of the different nations of the world. Herein, only a few passages from his description will be quoted. He begins his discussion with the following strong words,
"The sixth century of the Christian era, it is generally agreed, represented the darkest phase in the history of our race. Humanity had reached the edge of the precipice, towards which is had been tragically proceeding for centuries, and there appeared to be no agency or power in the whole world which could come to its rescue and save it from crashing into the abyss of destruction." 
After these words, he describes the plight of the Romans and the Persians, two of the major civilisations at that time. He said that they sunk "to a state of complete moral depravity. They wallowed in the inveterate vices of their corrupt and decaying civilisations." 
Perhaps religion could have been the saviour for the moral situation of the people of that time. However, Christianity, the main religion of the Western power, had lost most of its original teachings. Indeed, it had become so mixed with Greek mythology, Roman idolatry, Egyptian Neo-Platonism and Monasticism  that it itself was in need of help. For other similar reasons, Judaism and the Jews also were not in a position to offer much help to the prevailing situation.
The plight of Europe has been summed up by Robert Briffault in his The Making of Humanity,
"From the fifth to the tenth century Europe lay sunk in a night of barbarism which grew darker and darker. It was a barbarism far more awful and horrible than that of the primitive savage, for it was the decomposing body of what had once been a great civilisation. The features and impress of that civilisation were all but completely effaced. Where its development had been fullest, eg., in Italy and Gaul, all was ruin, squalor and dissolution." 
Shaykh Abul Hasan 'Ali Nadwi رحمه الله continues to discuss North-Western Europe, Iran, Central Asia (India) and China in some detail. He also discusses the religions of Buddhism, Hinduism and others. The plight of those areas and religions were similar to the plight of Europe and Christianity. It is sufficient, for the purposes here, to understand that mankind was definitely in a state of loss. There was no true light of guidance emanating from any part of the world at that time.
The plight of the Arabs was not much different from the rest of the world. However, their situation shall be dealth with in more detail as they are the people to whom the Qur'aan was first presented and they are the ones who were first most affected by its teachings.
The Arabs Before the Advent of the Prophet Muhammad (صلى الله عليه وسلم)
The Arabs - like all other peoples at that time - had a combination of virtues and vices. However, like the others, two dangerous characteristics were present: their vices were many and their virtues were distorted.
In the opening chapter of his The Life of Muhammad صلى الله عليه وسلم, Shaykh 'Abdul Hameed Siddiqui has presented an overview of the characteristics of the pre-Islamic Arabs. This overview is based on pre-Islamic poetry that described the common practices and beliefs of those days. Among their common features and attributes were: idol worship, love for sensuous pleasures, tribal pride, clan warfare, arrogance, disdain and lack of respect for women. 
For example, concerning their lust for sensual pleasures, Shaykh 'Abdul Hameed Siddiqui wrote,
"Drinking had in fact become a second nature with Arabs. Wine and women go together, and as a result of licentious drinking, fornication was very rampant. The caravans which radiated from Makkah with native merchandise to the Byzantine Empire, Syria, Persia and India, returned therefrom with all luxurious habits and vices and imported slave girls from Syria and Iraq who afforded vast opportunities of sensual pleasures to the rich with their dancing and singing and all corruption which usually goes with them. We reproduce below some of the verses which would give an idea of the immoral life which the Arabs of the pre-Islamic period were habituated to leade... 
The old Arab poetry has so many tales to narrate of the drinking orgies of the people of Arabia before the advent of Islaam... 
The heathen Arabs had little regard for the sanctity of matrimonial relations. They took pride in flouting them and describing publicly their adulterous adventures." 
Concerning the status of women in pre-Islamic Arabia, Shaykh 'Abdul Hameed Siddiqui wrote, again based on evidence from pre-Islamic poetry,
"Not only were the female infants buried alive, but those who were spared, led a life of unspeakable misery and wretchedness. They were a sort of marketable commodity which could be sold in the open market to the highest bidder. At the time they were transferred to the custody of their husbands their position was still worsened. Marriage for them was a kind of bondage and the marital rights of the husband were a kind of overlordship. He was free to treat and dispose of his property as he liked." 
The Change in the Arabs Brought about Through the Qur'aan, by the Will of Allaah سبحانه و تعالى
It is clear that the Arabs at the time of the Prophet صلى الله عليه وسلم were wont to drink, make merry and engage in tribal battles. They were knwon to sometimes kill their female babies. However, one finds that in a short span of close to twenty years a movement that started with just one man was able, due to the grace of Alaah سبحانه و تعالى and the miraculous effect of the Qur'aan, to change almost all of the Arabs and non-Arabs in the Arabian peninsula and bind them together into a brotherhood of faith and mercy which was so strong that if any part of this brotherhood was in anguish, the whole brotherhood would be affected negatively. At that time, one could find two people who were from previously antagonistic tribes sharing their wealth and willing to give up their lives for each other. Indeed, one was willing to split half of his wealth and divorce one of his wives for the sake of his new brother who was from a "foreign" tribe. 
Perhaps one of the best descriptions of the change that took place among them can be seen in the famous statement of the noble Companion Sayyiduna Ja'far Ibn Abi Taalib رضي الله عنه who was asked by the Negus of Abyssinia about the mission of the Messenger صلى الله عليه وسلم. He told him,
"O king, we were an ignorant people, worshipping idols, eating carrion and indulging in sexual pleasures. We teased our neighbours, a brother oppressed his brother, and the strong devoured the weak. At this time a man rose among us صلى الله عليه وسلم, who had already been known to be truthful, noble and honest. This man called us to Islaam. And he taught us to give up worshipping stones, to speak the truth, to refrain from bloodshed, and not to defraud the orphans of their property. He taught us to provide comfort to our neighbours and not to bring slander against chaste women. He enjoined upon us to offer prayers, observe fasts and give alms. We followed him, gave up polytheism and idolatry and refrained from all evil deeds. It is for this new way that our people have become hostile to us and compel us to return to our old misguided life." 
That generation, in turn, took the message to the rest of the world. They were clearly a people who were taken from darkness into light and to the straight path of Allaah. When asked by the Emperor of Persia what brought the Muslims to their lands, two different Companions answered in similar terms: "Allaah has sent us to take whoever wishes from the servitude of mankind to the servitude of Allaah and from the tightness of this world to its expanse and from the injustice of the ways of life [in this world] to the justice of Islaam." 
During the lifetime of the Prophet صلى الله عليه وسلم one can see how these people were turned into a pious generation, fearing Allaah سبحانه و تعالى and hoping for Allaah's سبحانه و تعالى reward. Even when they, as humans, slipped and committed sins, they eagerly repented and turned to Allaah سبحانه و تعالى for His forgiveness. They would much rather face a severe penalty in this life, such as death, than face Allaah with their sins on their hands. This can be seen in the cases of Maa'iz Ibn Maalik al-Aslami رضي الله عنه and the woman called al-Ghaamidiyah رضي الله عنها. Both of them came to the Prophet صلى الله عليه وسلم to admit that they had committed adultery and each asked the Prophet صلى الله عليه وسلم for the worldly punishment of stoning to death to erase their sins. In the case of al-Ghaamidiyah رضي الله عنها, the Prophet asked her to go back after her confession and to return to the Prophet صلى الله عليه وسلم after she had given birth. She came back with her child in her arms and asked the Prophet صلى الله عليه وسلم to purify her from her sins. The Prophet صلى الله عليه وسلم then asked her to return after she had weaned the child. Then she returned after some time and told the Prophet صلى الله عليه وسلم that the child was no longer in need of her breastfeeding. She once again asked for her expiation from her sin. Then, finally, the Prophet صلى الله عليه وسلم had a ditch dug for her and she was stoned to death as an expiation for her sin of adultery. The Prophet صلى الله عليه وسلم then praised her act of repentance. 
The effect of this change in the noble Companions رضي الله عنهم continued long after the death of the Prophet صلى الله عليه وسلم. Note the following accounts of the Companions as they sought to spread the message of Islaam to the rest of the world:
"The sterling character and qualities of the Muslim soldiers were once praised by a Roman officer in these words: 'At night you will find them prayerful; during the day you will find them fasting. They keep their promises, order good deeds, supress evil and maintain complete equality among themselves.' Another testified thus: 'They are horsemen by day and ascetics by night. They pay for what they ear in territories under their occupation. They are first to salute when they arrive at a place and are valiant fighters who just wipe out the enemy.' A third said: 'During the night it seems that they do not belong to this wolrd and have no other business than to pray. And during the day, when one sees them mounted on their horses, one feels that they have been doing nothing else all of their lives. They are great archers and great lancers, yet they are so devoutly religious and remember God so much and so often that one can hardly hear talk about anything else in their company.'" 
Why Doesn't the Qur'aan Have the Same Effect Today?
William Ewart Gladstone, four-time Prime Minister of Great Britain, is famous for telling the English Parliament, "As long as this Qur'aan exists, Europe will never be able to conquer the Islamic East." Similarly, the French Colonial Governor of Algeria said, on the occasion fo one hudred years of French occupation of Algeria, "It is a must to remove the Arabic Qur'aan from their presence and to remove the Arabic language from their tongues in order for us to have victory over them." 
Actually, many of the enemies of Islaam have perceived an even more important point: It is not necessary to physically remove the Qur'aan from the hands of the Muslims. They only need to remove the Qur'aan from being central to the life of the Muslim. It is possible for people - Muslims - to possess the Qur'aan and still not receive the benefits, guidance and blessings that should go hand in hand with the Qur'aan.
The reason why the Qur'aan does not have the same effect today has nothing to do with the essential nature of the Qur'aan - as it will always be the the true guidance that is ever available to take mankind from darkness into light. The source of the problem is in the way that many of today's believers approach the Qur'aan. The possible reasons for this kind of situation could be many. In general, though, four stand out glaringly:
(1) Some Muslims emphasise the secondary aspects of the Qur'aan while ignoring its more important primary aspects;
(2) Related to (1), too many Muslims do not recognise and understand the primary goals of the Qur'aan; therefore, they read it but do not get out of it what it desires for them;
(3) In addition, some Muslims do not approach the Qur'aan in the proper manner, missing the essential link between what it teaches and how it is to affect mankind; and
(4) Even when the above obstacles or problems are overcome, still some Muslims do not interpret the Qur'aan in the proper manner and, hence, although they read it they do not get its correct teachings from it.
These issues are truly the heart of the matter. 
 Imaam Ibn Katheer رحمه الله: Tafseer al-Qur'aan al-'Adheem, p. 574.
 See Shaykh Abul Hasan 'Ali Nadwi رحمه الله: Islam and the World (International Islamic Federation of Student Organizations, 1983), pp. 13-44. Shaykh Nadwi has also quoted a number of Western and non-Muslim sources that described the plight of mankind in the sixth and seventh centuries of the Christian era.
 Ibid., p. 13.
 Ibid., p. 14.
 Ibid., p. 17
 See Shaykh 'Abdul Hameed Siddiqui: The Life of Muhammad (Lahore, Pakistan: Islamic Publications, Ltd. 1975), pp. 4-36.
 Ibid., p. 15.
 Ibid., p. 17.
 Ibid., pp. 20-21.
 When the Muslims migrated to Madeenah, the Prophet صلى الله عليه وسلم established a bond of brotherhood between members of the new emigrants and members of the residents of Madeenah. Such a bond was established between Sayyiduna 'Abdur Rahmaan Ibn 'Awf رضي الله عنه, an emigrant from Makkah, and Sayyiduna Sa'd Ibn ar-Rabee' رضي الله عنه, one of the richest people of Madeenah. Sa'd رضي الله عنه offered to split his wealth with 'Abdur Rahmaan Ibn 'Awf رضي الله عنه and divorce one of his two wives so that he could marry one her. Sayyiduna 'Abdur Rahmaan Ibn 'Awf رضي الله عنه, also in a brotherly gesture, politely turned down Sayyiduna Sa'd's رضي الله عنه offer and asked him to point him to the market place wherein he could work to gain his own wealth and be able to marry on his own. (Recorded by Imaam al-Bukhaaree رحمه الله.)
 The translation of this statement was taken from 'Allaamah Shibli Nu'mani رحمه الله: Seeratun-Nabi (Lahore, Pakistan: Kazi Publications, 1979), p. 211. The incident was recorbed by Ibn Ishaaq in al-Maghaazi and Imaam Ahmad. Its chain is saheeh according to Shaykh al-Albaani رحمه الله. See Shaykh al-Albaani's رحمه الله footnotes to Shaykh Muhammad al-Ghazzaali رحمه الله: Fiqhus-Seerah (Qatar: Idaarah Ihyaa at-Turaath al-Islaami, n.d.), p. 126.
 Imaam Ismaa'eel Ibn Katheer رحمه الله: Al-Bidaayah wan-Nihaayah (Beirut: Dar al-Kutub al-'Ilmiyya, n.d.), vol. 7, pp. 39-40.
 The story of both Maa'iz رضي الله عنه and al-Ghaamidiyyah رضي الله عنها are recorded by Imaam Muslim رحمه الله.
 Quoted from Shaykh Abul Hasan 'Ali Nadwi رحمه الله: Islam and the World, p. 81. See also Imaam Ibn Katheer: al-Bidaayah wan-Nihaayah, vol. 7, p. 53.
 Shaykh Jamaalud-Deen Zarabozo: How to Approach and Understand the Quran, pp. 35-48.