Allah informs that He sent the Qur'an down during the Night of Al-Qadr, and it is a blessed night about which Allah says,
إِنَّآ أَنزَلْنَـهُ فِى لَيْلَةٍ مُّبَـرَكَةٍ
(We sent it down on a blessed night.) (44:3) This is the Night of Al-Qadr and it occurs during the month of Ramadan. This is as Allah says,
شَهْرُ رَمَضَانَ الَّذِى أُنزِلَ فِيهِ الْقُرْآنُ
(The month of Ramadan in which was revealed the Qur'an.) (2:185) Ibn `Abbas and others have said, "Allah sent the Qur'an down all at one time from the Preserved Tablet (Al-Lawh Al-Mahfuz) to the House of Might (Baytul-`Izzah), which is in the heaven of this world. Then it came down in parts to the Messenger of Allah ﷺ based upon the incidents that occurred over a period of twenty-three years." Then Allah magnified the status of the Night of Al-Qadr, which He chose for the revelation of the Mighty Qur'an, by His saying,
Ibn Abi Hatim has reported from Mujhid (as mursal hadith) that the Messenger of Allah ﷺ was told about a mujahid [ warrior in the cause of religion ] from amongst the Children of Israel who carried weapons of war on his shoulders for a thousand months during which time he never laid down his arms. The Companions were amazed when they heard this. On that occasion, this Surah was revealed which describes that worship in the Night of Qadr granted to this Ummah exceeds by more than a thousand months of jihad persistently fought by that warrior. According to another narration of Mujahid cited in Ibn Jarir, a worshipper from among the Children of Israel used to worship Allah the whole night, and as soon as the dawn broke, he would arm himself and fight the whole day. This continued consecutively for a thousand months. This Surah was thus revealed. This shows the superiority of the Ummah of the Holy Prophet `, and that the Night of Qadr is a special characteristic of this ummah. [ Mazhari ].
A particular night of the year (perhaps some night in the last days of the month of Ramadan) is the night of decisions by God. Certain tasks have to be performed in the course of the year in connection with the administration of the world, and the angels descend to the earth to arrange for them to be carried out. On a similar particular night, the revelation of the Quran began.
Uthmani text of the Madinah mushaf (King Fahd Complex). Translation: Saheeh International. Tafsir via Quran.com.