The term "Ruh" has different meanings in different fields of science, referring to a different meaning in each one. In the Quran, this term also has its own special meaning and has been mentioned in different ways.
Regarding the verse there are various opinions about which Ruh's essence the prophet is being enquired about: Ruh Heywani (the animal soul), Ruh Insani (human spirit; also known as Nafse Natiqah), Ruhul Qudus (the Holy Spirit), Gabriel or something that has a higher status than angels (which may also be called Ruh). What is for sure is that here, Ruh does not mean the animal soul that is mentioned in medical science, because learning about it is within the scope of science. Also the term cannot refer to Gabriel because the term Ruh has been mentioned in some verses next to the angels, which shows Ruh is something different than an angel; this is something that ahadith explicitly point out.
According to this verse all that can be said about the Ruh is that it is a Mojarrad (abstract and detached from material) being and a matter of Allah’s, and anything that is attributed and belongs to Allah (swt) is beyond time, place, matter or other physical limits.
Comprehending this divine being and understanding its levels is among the divine secrets that one can only learn of through disclosure; of course, one can be sure that the prophet was well aware of it. The reason why the prophet rejected to explain more about it was that the people did not possess the ability to comprehend his words about the Ruh and it would only make them confused. Therefore explicit descriptions of the Ruh are not mentioned in the Quran.
It became clear in the light of what was explained that because the Ruh is not a material substance and it is not limited within the boundaries of time and place therefore it can not be seen or sensed through physical senses, but some of its traces and appearances can take place through very light and subtle substance, namely the mithali body (imaginal body) which is the form the soul takes on in the Barzakh.
It is also noteworthy that in the common terminology of some sciences, and also according to some ahadith, this same mithali body is apparently also called Ruh, the reason being that this body is inhabited by the soul after its detachment from the material body, bearing more capacity to show traces of the soul. This mithali body can be seen in its own world, but it shouldn’t be mistaken with the Ruh that is a matter of Allah’s and attributed to him, because the Ruh is beyond all of these things and is of the divine secrets.
One of the major issues discussed in different religions, and in philosophy and mysticism, is the understanding of its link with man and the world. Theologians and Muslim philosophers have presented several opinions regarding the essence of the soul and some hadiths and Quranic verses have given some general information about it. But generally speaking, understanding the essence of the soul in its Quranic sense is beyond the scope of material sciences and scientists, therefore the only way to correctly understand it is through disclosure, as it has been said the knowledge of Nafs (ma’rifat nafs/self-knowledge) which is actually the knowledge of the Lord, is the knowledge of the essence of the soul.
2- What does the term "Ruh" refer to?
It must be noted that the word Ruh refers to different meanings depending on the science and field the term has been used in. In the Quran the Ruh refers to a unique meaning and has been used in different forms like "الروح", "روحی", "روحٌ منه", “روح الامین”, “روح القدس”, etc.
3- Ruh in verse 85 of Surah Al Isra'
One of the important verses of the Quran that briefly explains the essence of the soul is verse 85 from Surah Al Al Isra' in which the Almighty says: " یسألونک عن الروح قل الروح من امر ربی و ما اوتیتم من العلم الا قلیلاً"
"They ask thee concerning the Spirit. Say:" The Spirit is off the command of my Lord: of knowledge it is only a little that is communicated to you, (O men!)".
Regarding the verse there are various opinions about which Ruh's essence the prophet is being enquired about: Ruh Heywani (the animal soul), Ruh Insani (human spirit; also known as Nafse Natiqah), Ruhul Qudus (the Holy Spirit), Gabriel or something that has a higher status than angels (which may also be called Ruh). What is for sure is that here, Ruh does not mean the animal soul that is mentioned in medical science, because learning about it is within the scope of science. Also the term cannot refer to Gabriel because the term Ruh has been mentioned in some verses next to the angels (الملائکه و الروح), which shows Ruh is something different than an angel; this is something that ahadith explicitly point out. In his commentary on the Quran Al Mizan, Allameh Tabatabei says in regard to the essence of the soul in the verse "یسئلونک عن الروح......" : "It seems that the Ruh is a being greater than Gabriel and the other angels".
Some of the ahadith that clearly state that the Ruh is a being other than the angels and Gabriel are as follows:
1- " اتی رجل امیر المومنین (ع) یسأله عن الروح الیس هو جبرئیل فقال له امیر المومنین (ع): جبرئیل من الملائکه و الروح غیر جبرئیل " A man come to Imam Ali and asked: "Isn't the Ruh Gabriel?" the Imam replied: "Gabriel is an angel and the Ruh is not Gabriel".
2- عَنْ أَبِی بَصِیرٍ قَالَ سَأَلْتُ أَبَا عَبْدِ اللَّهِ (ع ) عَنْ قَوْلِ اللَّهِ عَزَّ وَ جَلَّ یَسْئَلُونَکَ عَنِ الرُّوحِ قُلِ الرُّوحُ مِنْ أَمْرِ رَبِّی قَالَ خَلْقٌ أَعْظَمُ مِنْ جَبْرَئِیلَ وَ مِیکَائِیلَ کَانَ مَعَ رَسُولِ اللَّهِ ص وَ هُوَ مَعَ الْأَئِمَّةِ وَ هُوَ مِنَ الْمَلَکُوتِ"
Abi Baseer asked Imam Sadegh about the verse in the Quran that says " یسئلونک عن الروح قل الروح من امر ربی " The Imam responded: "It is a being greater than Gabriel and Mika’il, it would stay with the prophet and now it stays with the Ahlul-Bayt, it is a being from the realm of "Malakoot".
However some verses indicate that the Ruhol Amin is Gabriel. Allameh Tabatabaei has reconciled between these two matters in such manner: In his tafsir he says: "The Quranic verses indicate that Gabriel and Mika’il are the carriers and transporters of the Ruh and as a result accompany the Ruh in all its descending and ascension. Therefore from one perspective the Ruh is attached to the Angels and Gabriel while from another it is separate from them."
4- The essence of the Ruh according to the Quran and verse 85 from Surah Al Isra’
In this verse the almighty briefly points out the essence and quiddity of the Ruh: " قل الروح من امر ربی قل الروح من امر ربی " "The Spirit is of the command of my Lord". In order to understand the "Amrollah" (command of the Lord) and what features it has we must refer to the other verses in the Quran that relate to the command of Allah like this verse: " انما امره اذا اراد شیئاً ان یقول له کن فیکون " " All his command, when he wills something, is to say to it " Be," and it is."
From Allamah Tabatabai’s standpoint in Tafsir Al-Mizan, this verse shows that the Ruh is of the command of Allah and is associated with His entity, and since the command of the Lord is made up of the word “کن” (be) which is the word used for creating and indicates the action that solely belongs to Him, the Ruh which is also of His command, can in no way be measured by time and place or any other physical measurement.
In the Quran the almighty has referred to the Ruh in different ways, sometimes it has been mentioned alone, sometimes it has been mentioned alongside the angels, sometimes it means the substance that has been breathed into every human being, sometimes it is the being that accompanies the believers and helps them and sometimes it means the truth that the prophets are in touch with.
5- How come a deeper explanation was not given about the essence of Ruh?
In brief, what can be said about the Ruh is that it is a Mujarrad (abstract/devoid of substance and material) being and is of the command of Allah, but the deep comprehension of this divine being and understanding it's levels is among the divine secrets. The reason why the prophet rejected to explain more about it was that the people did not possess the ability to comprehend his words about the Ruh and it would only make them more confused or even bring about misguidance, therefore explicit and detailed descriptions of the Ruh have not been mentioned in the Quran.
Knowing the reason why the prophet did not speak of the Ruh much, we shouldn’t think that he himself didn’t have knowledge of it, the same way great mystics throughout history may have had knowledge of the Ruh through spiritual and divine disclosure, but wouldn’t speak of its secrets to those whom these secrets had been hidden from and not transmitted to, because there would be no benefit in it.
As for its meaning, it seems that the part of the verse that follows (و ما اوتیتم من العلم الا قلیلا) means that what those possessing knowledge of the material world is almost nothing compared to what there actually is, and that the essence of the Ruh goes beyond such, and to understand it divine visions and disclosures are needed.
6- Can we see the Ruh? Is it visible?
From what was said, it becomes clear that since the Ruh is a truth beyond time and place and other material characteristics, hence it isn't tangible through normal senses, although knowledge of it is possible for the infallibles and maybe even for some great arefs and mystics, all of this being through disclosure and divine inspiration (and still not being in conflict with the abstractness of the Ruh). Also, some of the Ruh’s manifestations and traces (not its essence itself) can take on the form of light and subtle substances and appear through them, namely the mithali body, which the soul takes on in the Barzakh; this body shares some of the characteristics of the material body but to a higher degree of light and subtleness.
It is also noteworthy that in the terminology of some sciences and also even in some ahadith, this mithali body has been called Ruh as well, the reason being that it is this body that carries the soul after death and its detachment from the material body. This body bears more potential to show traces of the soul than the material body. It isn't an absolute mojarrad (abstract) being, thus allowing it to be seen through vision and disclosure. At the same time though, this body shouldn’t be mistaken for the true Ruh and its essence, which is attributed to Allah (swt) and is of the command of Allah (swt), because there is a great difference and the true Ruh is way beyond these matters in this world and is of the divine secrets.
 Ahmad ibn Muhammad Husein Ardekani, Mir’at Al-Akwan (Tahrir of Sharh Hidayah of Mulla Sadra), pg. 37.
 Isra:85; Ghafir:15.
 Hajj:29; Sad:72.
 Mujadalah:22; Nisa:171.
 Baqarah:87 and 253; Ma’idah:110; Nahl:102.
 Koleini, Kafi, vol. 1, pg. 274.
 Kafi, vol. 1, pg. 273.
 Tabatabai, Seyed Mohammad Hosein, Al-Mizan, Musavi Hamedani, Seyed Mohammad Baqir, vol. 13, pp. 171-172.
 Al-Mizan, vol. 1, pp.528-529.
 Mir’at Al-Akwan, (Tahrir of Sharh Hidayah of Mulla Sadra), pg. 36.