In the name of Allah(swt) the most beneficient, the most merciful.
If you believe and follow Islam, you need to have proof it is from God. There are just so many ways you can support the inevitible argument that Islam is indeed from Allah swt. However, we need to go back and think about how Allah swt wants us to address this issue.
Quran: "And if you are in doubt about what We have sent down upon Our Servant [Muhammad], then produce a Surah the like thereof and call upon your witnesses other than Allah , if you should be truthful."
Even from the time of Muhammed pbuh, people tried to challenge and match the Quran. The fact Muhammed pbuh succeeded does lend some evidence that his challenge was not met - because he would easily have been countered as a lier by the arabs, who were at the peak of their linguistic powers and prided themselves on this.
The Quran is matchless not only in language, but depth, meaning , reach, historical statements, prophecies, morals, refereal to scriptures, and (not to say there are 'scientific miracles') but verses of natural phenomenon, when translated within the limited scope of the arabic language, suggest profoundly accurate statements.
However , let me focus on the language, because this is the primary challenge to the arabs. You might feel as though muslims naturally would have some sort of 'bias' (this itself is false, because we can objectively deduce the superiority of the Quran and explain it), but never the less, here are the words of Non-muslims.
Here are the words of Non-Muslims about the Quran(including translators):
"From the literary point of view, the Koran is regarded as a specimen of the purest Arabic...It has been said that in some cases grammarians have adopted their rules to agree with certain phr ases and expressions used in it, and that though several attempts have been made to produce a work equal to it as far as elegant writing is concerned, none has as yet ucceeded"
F.F. Arbuthnot, The Construction of the Bible and the Koran, London 1885, p5
It is confessedly the standard of the Arabic tongue... The style of the Koran is generally beautiful and fluent... and in many places, especially where the majesty and attributes of God are described, sublime and magnificent ... He succeeded so well, and so strangely captivated the minds of his audience, that several of his opponents thought it the effect of witchcraft and enchantment.
George Sale, The Koran: The Preliminaiy Discourse, London, 1891, p47 48
The truth is I do not find any understanding author who controverts the elegance of the Al Qur'an, it being generally esteemed as the standard of the Arabic language and eloquence.
Dr. Hency Stubbe MA, Rise and Progress of Mohammadanism, London 1911, p158
All those who are acquainted with the Qur'an in Arabic agree in praising the beauty of this religious book; its grandeur of form is so sublime that no translation into any European language can allow us to appreciate it.
Edward Montet, Traduction Francaise du Coran, Paris 1929, Introduction p25
Briefly, the rhetoric and rhythm of the Arabic of the Koran are so characteristic, so powerful, so highly emotive, that any version whatsoever is bound in the nature of things to be but a poor copy of the glittering splendour of the original... My chief reason for offering this new version of a book which has been "translated" many times already is that in no prev ious rendering has a serious attempt been made to imitate, however imperfectly, those rhetorical and rhythmical patterns which are the glory and the sublimity of the Koran.
The Koran Interpreted by Arthur J. Arberry, London 1980, Preface p24 25
NOTE: A.J Arberry, the British Orientalist, was professor of Arabic at Oxford University
The Koran is the earliest and by far the finest work of Classical Arabic prose... It is acknowledged that the Koran is not only one of the most influential books of prophetic literature but also a literary masterpiece in its own right... translations have, in my opinion, practically failed to convey both the meaning and the rhetorical grandeur of the original.
The Koran Translated with Notes by N. J. Dawood, 5th Edition 1990, pp1,3
NOTE: Nessim Joseph Dawood is a Jewish Iraqi Scholar
Indeed, throughout history, many Arab Christians as well have regarded it as the perfection of Arabic language and literature.
John L. Esposito, Islam: The Straight Path, Oxford University Press, 1991, p21
NOTE: This author is Professor of Religion at the College of the Holy Cross