Literally meaning perception intelligence discretion evidence and witness insight (basira) is defined as having an eye of the heart open deep perception an ability to see consequences just at the beginning of an act or foresight. Insight acquires a different deeper dimension among Sufis.
It is considered the sole source of spiritual knowledge obtained through reflective thought and inspiration the first degree in the spirit's perception of the reality of things; and a power of conscience that discerns and establishes values originating in the spirit whereas reason becomes entangled in colors forms and qualities. It is also a power of perception so sharpened by the light of nearness to the Divine Being that when other powers of perception become exhausted by imaginings it acquires great familiarity with mysteries lying behind things and without any guide or evidence reaches the Truth of the Truths where reason is bewildered.
Seeing is one of the luminous Attributes of God Almighty and one's insight as declared in: We have shared among them (43:32) is proportionate to one's ability to receive the manifestations of this Attribute. The greatest portion belongs to the one who having benefited from that Divine Source to the fullest poured his inspirations into the hearts of his followers namely the Prophet Muhammad upon him be peace and blessings. He is the most polished mirror of the Truth's manifestations and is unequaled in receiving them. The Divine declaration: Say: This is my path. I call to God on clear evidence and by insight. I and whoever follows me (12:108) points to the greatness of the share of that Divine gift belonging to the prince of the Prophets and his followers.
This matchless perceptiveness allowed that holy traveler on the path of Ascension to reach in one breath the realms beyond corporeal existence which those devoid of even the least perception regard as dark or unknown or categorically deny. He studied those realms like a book and traveled on the "slopes" of the Unseen where the archetypal tablets are exhibited and the melodies of the pens of Destiny which make one's heart jump thrilled him. He visited Paradise accompanied by heavenly male and female servants and received a Divine welcome with the breaths of two bows' length or even nearer (53:9) at a point where space and location are undefined or undifferentiated.
The pleasure of observance given by insight sometimes acquires a new deeper dimension when the believer begins to discern and discover the spiritual dimension and meanings of things and events. His or her spirit experiences other dimensions in this three-dimensional realm and his or her conscience becomes the eye of existence with which it sees as well as its pulse and intellect.
In addition to perception and understanding discernment (firasa) denotes the deepening of insight when perception becomes a source of certain knowledge. Those who discern the manifestations of the light of God the Truth own such a radiance that they see everything every issue in its full clarity. They are never confused even when encountering the most intricate similar elements and are not lost in particularities. Seeing at the same time for example sugar with the sugar cane and hydrogen and oxygen with water they refrain from all deviation (e.g. pantheism and monism) and recognize the Creator however He is and the created however it is.
From the face of each individual believer to the face of the universe every point word and line in existence is a meaningful message even a book for those to whom the verse: Surely in this are signs for those having insight and discernment (15:75) refers. Those who can look at existence from a point stated in the Prophetic Tradition of: Fear the discernment of a believer for he sees with the light of God.  make contact with reality become familiar with the invisible side of existence and revealing the real face of everything shed light on events. While some spend their lives in "black holes" they are enraptured with increasing pleasures on Paradise-like "slopes."
For one endowed with such discernment existence is a book of countless pages with each animate or inanimate part of creation being a word shining with thousands of meanings and the face of existence and each person expressing many hidden realities. Those of true spirituality see such things in the "verses" of that book and in the luminous "phrases" of those verses and receive from them messages that even the greatest minds among the non-believers are unable to discern. The unimaginable surprises awaiting believers in the other world are according to the rank of each and are revealed to them together with all the spiritual pleasure that they give.
 Al-Tirmidhi. "Tafsir al-Qur'an" 6.