Praise be to Allah.
Undoubtedly the Qur’aan is miraculous, and there are many facets to its miraculous nature, such as linguistic, legislative, and so on. Its challenge to mankind and the jinn to produce something similar to it still stands. Allaah says (interpretation of the meaning):
“Say: If the mankind and the jinn were together to produce the like of this Qur’aan, they could not produce the like thereof, even if they helped one another”
Ibn al-Qayyim discussed the number 7 in his book Zaad al-Ma’aad fi Huda Khayr al-‘Ibaad (4/90) when he discussed the hadeeth in al-Saheehayn: “The one who eats seven dates of al-‘Aaliyah in the morning will not be harmed that day by poison or witchcraft.” He said: As for specifying the number seven, it has to do with the creation and sahr’i commands of Allaah. Allaah created seven heavens, seven earths and seven days, and man’s creation is completed in seven stages; Allaah has prescribed that His slaves should walk around the Ka’bah seven times (tawaaf) and go back and forth between Safa and Marwah seven times (saa’i), and stone the jamaraat with seven pebbles each, and the takbeeraat of Eid are seven in the first rak’ah. The Prophet (peace and blessings of Allaah be upon him) said: “Instruct your children to pray when they are seven.” When the boy reaches the age of seven he should be given the choice between his parents according to one report, and according to another report, his father has more right to him than his mother; according to a third report his mother has more right to him. When he was sick, the Prophet (peace and blessings of Allaah be upon him) ordered that water from seven skins be poured on him. Allaah sent the wind against the people of ‘Aad for seven days. The Prophet (peace and blessings of Allaah be upon him) asked Allaah to help him by sending upon his people seven (years) like the seven years of Yoosuf – i.e., seven years of famine. Allaah likened the reward of one who gives charity to a grain that produces seven ears, in each of which are one hundred grains. The number of ears of grain seen by the companion of Yoosuf (in the dream) was seven, the number of years for which they were cultivated was seven, and (the reward for charity) is multiplied seven hundred fold or more. Seventy thousand of this ummah will be admitted to Paradise without being brought to account.
Then Ibn al-Qayyim commented: Undoubtedly this number has some special qualities that are not shared by other numbers. … Allaah knows best about His wisdom, laws and decree in singling out this number. End quote.
Based on this, the correct view is to refrain from indulging in discussion of the reason why this number is singled out for mention, except on the basis of clear, sound evidence.
For more information please see the answer to question no. 69741.
And Allaah knows best.