Corbin, the foremost French (and, in all probability, world) authority on Sufism and Shiite esotericism, discusses in his familiar baroque and stream-of-consciousness erudite style three Iranian sages-mystics: Suhrawardi (the martyred founder of Ishraqi/Illuminative school of Islamic esotericism ), Kubra (the founder of an influential Sufi order) and Simnani (an orthodox Sufi master who left behind a voluminous corpus of esoteric writings). What do these men have in common ?
At least, two things:
They all developed variants of highly imaginative multilayered metaphysics (especially Suhrawardi) and set up "theoretical" framework which was later used to interpret spectacular (one might blasphemously say "Cecildemillean" or LSD-like) visionary experiences.
Another common "trademark" is the Man of Light , the "inner man" who is the projection of (Arch)Angel Gabriel, or Supreme Spirit (Ar-Ruh al-Qudsi), or the Perfect Nature: in short, everyone's "True" or Higher Self.
One might add that the three mystics have been differentiated-dualists (therefore, alien to Ibn Arabi's monist Wahdat-al-Wujud doctrine), and that the latter duo (in sharp contrast to the extravagant and highly original visionary genius of mutilated Suhrawardi ) remained impeccably orthodox. Their originality lies in the development of Islamic version of esoteric physiology: latifa, the supposed organs/subtle centers of suprasensory perception, are essentially Kubra's and Simnani's spiritual legacy.
Ironically, the central image of the entire opus comes not from Iran, or Sufism of any variety- but from the heterodox Gnostic writings of the 3rd century C.E. Greek- Egyptian alchemist Zosimos & a few other Gnostic scriptures, including Mary the Prophetess' sayings; a parable on two brothers: Prometheus Phos, the Light and Knowledge radiating Neoplatonized Prometheus from Hesiod and Plato- just transformed from a Titanic personality to a Titanic principle, and his twin brother Epimetheus, the latter succumbing to the pleasures of this world which envelop and hypnotize him into stupor, sexuality and dream. Brothers are presented as polar forces or quasi- beings of diverging energies inhabiting the nuclear spiritual self, the Man of Light passing through the Odyssey of physical incarnation. Prometheus Phos is, in his battle for individual entity's spiritual destiny, aided by the Nous, the true Self whose radiance or "ray" he is. In Arabic Hermetic texts from the 10th and the 11th centuries C.E., this "Higher Self" (modern, New Age parlance) is called al-tiba' al-tamm; in other traditions related to the Gnostic and Hermetic worldviews - Nous, Pneuma (Pagan Greek), Christ, the Son (Neoplatonic Christianity), Ar-Ruh Al- Qudsi, Nur-i- Muhammadi (variants of Islamic Sufism), Adam Kadmon (Lurianic Kabbalah in Judaism) or the triple principle Yechida-Chaya-Neshama. Other portions of the book include Green Light, Heavenly witness, supra-sensory organs of perception, Goethean science on "physiological colors" (dated and wacky) etc. Corbin's presentation is replete with examples from Zoroastrian mythology and mythic psychology, Gnostic Christian and Hermetic traditions.
This is what differentiates Gnosis from other forms of spiritual psychologies that go beyond the psyche. In Advaita and in Zen/Ch'an, you have only the Self which is equal to the Being. In more nuanced doctrines of Philosophia Perennis, you encounter both self, which is the entity, and the Self, which is the source of that entity. So, in the Vajrayana Buddhism, you have shes-pa and rig-pa or in Sanskrit, vijnana/the principle of consciousness & the Buddha Nature/Buddhata; in the Rhineland school of Neoplatonic Christianity, you have "scintilla animae" or fuenklein/spark & inner Christ Logos; in the Neo-Confucian/Taoist synthesis, this is the case with shen/spirit or "pearl" & the Original Nature/Hsin; in Hermetism, it is the Man of Light (Photeinos Anthropos) & the Perfect Nature (Natura Perfecta, in Greek Mind/Nous); in non-Advaita variants of Vedanta, it is jiva & Atman; in Christian Gnosticism it is the spiritual seed/sperme pneumatike and Angel Christ/Angelos Christos ...
Advice: the central chapter is 2, the rest may be only cursorily read.