The Qur'an's substance is a compelling argument for its divine authorship. Those who allege that someone wrote it provide no proof to support their assertion. Other Scriptures, due to human intervention, make claims that we know to be untrue. For example, they give a particular account of creation or of a natural phenomenon (for example, the Flood), which we know from modern scientific facts, such as fossils or astronomic discoveries, to be false. People altered those Scriptures to suit their own understanding, with the result that the progress of science has rendered their understanding and their now-corrupted Scriptures largely irrelevant and obsolete. However, the Qur'an has not been subject to such mistreatment.
If someone wrote the Qur'an, how could it be literally true on matters that were completely unknown at the time of its revelation? For example:
[Do not the unbelievers realize that the Heavens and the Earth were one unit of creation before we split them asunder?] (Al-Anbiyaa' 21:30)
Only in the last few years have we been able to contemplate this verse about the first moment of the universe in its literal meaning.
Similarly, when we now read
[God raised the Heavens without any pillars that you can see … He has subjected the sun and moon [to a law]; each runs its course for a term appointed. He regulate all affairs, explaining the signs in detail, that you may believe certainly in the meeting with your Lord] (Ar-Ra`d 13:2)
we can understand the invisible pillars as the vast centrifugal and centripetal forces maintaining the balance amid the heavenly bodies. We also understand from this and related verses (55:5; 21:33, 38, 39; and 36:40) that the sun and moon have fixed life-spans, that their force of light has faded or will fade away, and that they follow orbits that have been determined with the most minute exactness.
A literal understanding of these verses does not diminish the responsibility that comes with understanding — that you may believe certainly in the meeting with your Lord. The purpose of the verses has not changed; only our knowledge of the phenomenal world has changed. In the case of former Scriptures, scientific progress has made their inaccuracies ever more visible and their associated beliefs ever more irrelevant. Just the opposite is true with the Qur'an — scientific progress has not made even a single verse harder to believe or to understand. On the contrary, such progress had made many verses more understandable.
Yet some people still allege that the Prophet wrote the Qur'an. While asserting that they are on the side of sense and reason, they allege what is humanly impossible. How could a seventh-century man know things that only recently have been accepted as scientifically established truths? How is that humanly possible? How is it on the side of reason and sense to claim such a thing? How did the Prophet discover, with an anatomical and biological accuracy only recently confirmed, that milk is produced in mammal tissues? How did he discover how rain clouds and hailstones form, or determine a wind's fertilizing quality, or explain how landmasses shift and continents form and reform? With what giant telescope did he learn of the universe's ongoing physical expansion? By what equivalent of X-ray vision was he able to describe in such great detail the different stages of an embryo's evolution within the uterus?
Another proof of the Qur'an's divine origin is that what it predicts eventually comes true. For example, the Companions considered the Treaty of Hudaibiyah a defeat; the revelation stated that they would enter the Sacred Mosque in full security and that Islam would prevail over all other religions (48:27-28). It also promised that the Romans [Byzantines] would vanquish the Persians several years after their utter defeat in 615 (30:2-5) and the Romans did.
Although the Prophet was the ideal man, he could make mistakes on matters not related to Islam or revelation. For example:
• When he exempted certain hypocrites from jihad, he was criticized:
[God forgive you! Why did you let them stay behind before it became clear for you which of them were truthful and which were liars?] (At-Tawbah 9: 43)
• After the Battle of Badr, he was rebuked:
[You (the believers) merely seek the gains of the world whereas God desires [for you the good] of the Hereafter. God is All-Mighty, All-Wise. Had there not been a previous decree from God, a stern punishment would have afflicted you for what you have taken] (Al-Anfal 8:67–68)
• Once he said he would do something the next day and did not say "if God wills." He was warned:
[Nor say of anything, I shall be sure to do so-and-so tomorrow, without adding "if God wills." Call your Lord to mind when you forget, and say: "I hope that my Lord will guide me ever closer than this to the right way.] (Al-Kahf 18:23–24)
• When he swore that he would never again use honey or drink a honey-based sherbet, he was admonished:
[O Prophet. Why do you hold to be forbidden what God has made lawful to you? You seek to please your wives. But God is Oft-Forgiving, Most Merciful.] (At-Tahrim 66:1)
In other verses, when the Prophet's higher duties and responsibilities are brought into clear focus, the limits to his authority are made known. There is a clear space between the Messenger and the message revealed to him, as clear as between a person and his or her Creator.