Everything has four modes of existence: verbal existence, written existence, mental existence and external existence. Revelation also has these four modes of existence: For example, when we speak of the external existence of the Quran we say that this Quran was received with these same words by the Prophet through revelation. Thus, the Quran enjoys a reality which is the Qur'an's objective and undifferentiated existence. This form of existence is devoid of word, letter and verse, and when this same reality becomes distinct, thereupon it becomes a reality having words, limits and forms. This stage of distinct and clear existence is also of two forms: The revelation of the Quran in one piece or as a whole which took place on the night of Qadr (Grand Night), and gradual revelation which took place during the 23 years of the propehthood of Prophet Muhammad – peace be upon him and his family. To put it clearly, we produce the following example: When a pen is filled with ink, it is the stage of ambiguity and undifferentiation, and when the inked pen begins to inscribe the undifferentiated reality into words, it is the stage of differentiation and distinction. On the Grand Night, the things that constituted unity and absolute simplicity were separated from each other and descended in the form of limits, forms and characteristics.
Hence, the Quran was also revealed as a whole to the Holy Prophet (s) on the night of Qadr, albeit in the form of words and with differentiated details. Therefore, the degrees of the descent of the Quran are: The stage of decisiveness, the instantaneous differentiation, the gradual differentiation.
The written existence of the Quran is the words which are available to us and which we have access to. The verbal existence of the Quran is the oral recitation of the Quran by reciters ranging from the Infallibles and angels to the general public. The mental and scientific existence of the Quran is also divided into a few types as shall be mentioned in the detailed answer to follow.
As everything has four modes of existence (verbal existence, written existence, mental existence and external existence), the divine revelation also has four modes of existence:
A) The written existence of the Quran is the apparent and visible writing.
B) The verbal existence of the Quran is the recitation of the Quran by reciters ranging from the Infallibles and angels to the general public.
C) The mental (subjective) and scientific existence of the Quran is also divided into a few types: The mental existence being in the soul, the existence which descends from the world of the Divine Command (Aalam al-Amr) upon the Prophet's heart at God's order. Referring to the same mode of existence, the Quran says:
"نَزَلَ بِهِ الرُّوحُ الْأَمِینُ عَلى قَلْبِکَ لِتَکُونَ مِنَ الْمُنْذِرِینَ"
"With it came down the spirit of Faith and Truth, * To thy heart and mind, that thou mayest admonish."
The Quran speaks of the hidden meanings which are revealed to the reciter when he recites the Quran:
"بَلْ هُوَ آیاتٌ بَیِّناتٌ فِی صُدُورِ الَّذِینَ أُوتُوا الْعِلْمَ"
"Nay! these are clear communications in the hearts of those who are granted knowledge."
D) The objective and undifferentiated existence which is the reality of the Quran originating in the divine source as it says: "(This is) a Book, with verses basic or fundamental (of established meaning), further explained in detail." The objective and external reality of the Quran is that which becomes a faithful Muslim's companion in the grave and which is incarnated in the Hereafter speaking and interceding for him with God.
Seyyeda Nusrat Amin, better known as Esfahani Lady, says, "Do not think that the reports about the Qur'an's intercession in the Hereafter is a mere proverb which should be interpreted for a meaning other than that which is apparent, because the Quran manifests itself somehow at every degree of existence and it has been demonstrated in its own place that the worlds of existence are longitudinal in the sense that they are not at the same level. Hence, every lower degree of existence is a depiction or insignia of the higher stage growing and developing in its light. Our world in which we are living is the lowliest of the degrees of the worlds of existence. This world is not but a "shell world", a surreal (figurative) one as compared to the higher world. There is the intermediate world above our world. It is the world in between this world and the world of resurrection. The intermediate world is the world forms and ideas, and the world above that world is the world of resurrection which is the world of comprehensiveness, truth and reality. That is the ultimate point of man's journey. One of the names of resurrection or the day of judgment is "Al-haqqah" (الحاقة) which signifies truth and reality. It is the day in which the non-manifest and innermost secrets of things become visible: "یَوْمَ تُبْلَى السَّرائِرُ" [It is the day in which the secrets are made manifest.] It is also the world of eternal life as the Quran says:
"وَ إِنَّ الدَّارَ الْآخِرَةَ لَهِیَ الْحَیَوانُ لَوْ کانُوا یَعْلَمُونَ"
"What is the life of this world but amusement and play? But verily the Home in the Hereafter,- that is life indeed, if they but knew."
Therefore, it is very likely that the Quran might appear in the grave and in the intermediate world (which is the world of form and idea) in its spiritual form as an intimate companion of the reciter. Also in the resurrection world which is the world of truth and reality, the objective existence of the Quran which has descended from the world of reality is likely to speak and intercede with God for the petitioner or insult those who have insulted it. Since, the resurrection world is the world of comprehensiveness and truth, whatever is considered in this world to be of accidents ('awaridh) will appear with their essential realities on the Day of Resurrection. In this world, our deeds and actions do not appear to be anything more than accidents. However, in the intermediate world, they appear in forms and on the Day of Resurrection they immerge in their objective reality together with their essential properties and effects. There are many verses and reports which indicate that man's actions acquire forms in the grave. If the actions are good, they appear in good forms and if they are bad, they appear in bad and ugly forms and they keep hurting and tormenting their possessors (doers) until the Day of Judgment. In addition, rational arguments also confirm what the prophets and divine leaders of mankind have reported.
Thus, the Quran has a reality which is its objective and undifferentiated existence. This form of existence is devoid of word, letter and verse, and when this same reality becomes distinct, then it becomes a reality having words, limits and forms. This stage of distinct and clear existence is also of two forms: The revelation of the Quran as a whole or in one piece which took place on the night of Qadr (Grand Night), and gradual revelation which took place during 23 years of the propehthood of Prophet Muhammad – peace be upon him and his family.
To put it clearly, things come into being with God's decree in two stages: A) Ihkaam (to make decisive) B) Tafsil (differentiation and distinction). It should be noted that explicit and firm things turn into differentiated objects on the Night of Qadr. The Quran also has immerged out from Ihkaam stage into the differentiated stage and becomes understandable for mankind. That is to say, the Quran has descended twice in differentiated form: The revelation of the Quran as a whole or in one piece which took place on the night of Qadr (Grand Night), and gradual revelation which took place during the 23 years of the propehthood of Prophet Muhammad (pbuh).
In any case, when the Quran was revealed in plain and detailed form, the Prophet (s) received the Book with these same words through revelation. At the Ihkaam stage which is the stage of ambiguity and undifferentiation, there is no word, letter or verse. This is like a pen filled with ink but when the inked pen begins to put the undifferentiated reality into words, it is the stage of differentiation and distinction. On the Grand Night, the things that constituted unity and absolute simplicity are separated from each other and revealed in the form of limits, forms and characteristics.
It has been clear from the above that the ontological degrees of the descent of the Quran are: The stage of decisiveness, the instantaneous differentiation, the gradual differentiation. In fact, there are some exegetes of the Holy Quran who have another explanation in this regard. They say that in the first stage, the words from "b" of "Bismillah …." to "s" of "an-Nas" have been created by God and it is called "God's Speech". Then it was inscribed by pen in the Protected Tablet. The Quran says:
"بَلْ هُوَ قُرْآنٌ مَجِیدٌ فِی لَوْحٍ مَحْفُوظٍ".
Nay, this is a Glorious Qur'an, (Inscribed) in a Tablet Preserved!
At the third stage, the Quran was revealed in the world of lights. The Quran says:
"إِنَّهُ لَقُرْآنٌ کَرِیمٌ فِی کِتابٍ مَکْنُونٍ لا یَمَسُّهُ إِلَّا الْمُطَهَّرُونَ تَنْزِیلٌ مِنْ رَبِّ الْعالَمِینَ"
"That this is indeed a qur'an Most Honorable,* In Book well-guarded, * Which none shall touch but those who are clean:* A Revelation from the Lord of the Worlds."
Thereupon the angle brought down the Quran on the night of Qadr in Baitul Ma'moor or the first heaven. Thereafter Gabriel brought down the Quran during the 23 years verse by verse, chapter by chapter as the Quran says:
: "وَ إِنَّهُ لَتَنْزِیلُ رَبِّ الْعالَمِینَ نَزَلَ بِهِ الرُّوحُ الْأَمِینُ عَلى قَلْبِکَ لِتَکُونَ مِنَ الْمُنْذِرِینَ".
"Verily this is a Revelation from the Lord of the Worlds: With it came down the spirit of Faith and Truth- To thy heart and mind, that thou mayest admonish."
 - Al-Shu'ara: 193
 - Al-Ankabut: 48
 - Hud: 1, See: Dawar Panah, Abulfazl, Anwar al-Irfan fi Tafsir al-Qur'an, vol.1, pg. 13, Sadr Publications, Tehran, 1996, first edition, with little modification.
 - Al-Ankabut: 64
 - Banu Esfahani, Seyyeda Nusrat Amin, Makhzan al-Arefeen in the Exegesis of the Quran, vol.1, p. 15 – 17, Muslim Women's Movement, Tehran, 1982, with little modification.
 - فیها یُفْرَقُ کُلُّ أَمْرٍ حَکیمٍ؛ دخان In the (Night) is made distinct every affair of wisdom, [Al-Dukhan: 4]
 -" (This is) a Book, whose verses are made decisive, then are they made plain, from the Wise, All-aware." [Hud: 1]
 - In this regard, see: Mutahhari, Morteza, Understanding the Uniqueness of the Quran, vol.5, pg. 101 – 105; Al-Mizan (Farsi Translation), vol.20, pg. 559 – 569; Ibid. vol.18, pg. 196 onward.
 - Burooj, 21 and 22.
 - Waqia: 76 – 79.
 - Al-Shu'ara: 192 – 194. See: Tayyid Sayyed Abdul Hussein, Atyabul Bayan fi Tafsir al-Quran, vol.13, pg. 177; Ibid vol.1, pg. 68 – 70, Islam Publications, Tehran, 1999, second edition.