We should now look at two mystical terms which, in Isaac the Syrian, point to an action of divine grace upon a person: ‘overshadowing’ and ‘illumination’. Isaac’s mysticism of light related to the idea of illumination, should also be considered here.

            The term maggnanuta,[1] which can be translated as ‘overshadowing’ or ‘tabernacling’, refers to a certain specific action of a higher power upon a lower. In Isaac, ‘overshadowing’ is the influence of the Holy Spirit over a person. This theme is discussed in a separate chapter.[2] It begins with the definition of the term and indications concerning its use in the Bible: 

‘Overshadowing’ is a term indicating help and protection, and also the receiving of a heavenly gift; for example, ‘The Holy Spirit shall come and the Power of the Most High shall overshadow you’.[3] The former kind is involved in ‘Cause Your right hand, Lord, to overshadow me’,[4] which is a request for help; this is like ‘I will overshadow this town and deliver it’.[5] Thus we understand two kinds of action in the ‘overshadowing’ over human beings that comes from God: one is mysterious (sacramental) and spiritual (noetic), the other practical.[6] 

            The first kind of overshadowing, continues Isaac, ‘consists in the sanctification which is received through divine grace; in other words, when, through the operation of the Holy Spirit, someone is sanctified in his body and soul, as was the case with Elisabeth, John the Baptist and the holy Mary, blessed among women - although in her case it was unique, going beyond the case of other created being’. Similar overshadowing happens with every saint who is deemed worthy of divine revelation and the action of the Holy Spirit: 

The mysterious variety of overshadowing such as takes place with any holy person, is an active force which overshadows the intellect, and when someone is held worthy of this overshadowing, the intellect is seized and dilated with a sense of wonder, in a kind of divine revelation. As long as this divine activity overshadows the intellect, that person is raised above the movement of the thoughts of his soul, thanks to the participation of the Holy Spirit... This is the partial overshadowing... of which those are held worthy who have received from the Spirit sanctification of the intellect through their holy and excellent way of life.[7] 

            As to the second kind of overshadowing, its activity becomes known to a person from practice, and it is ‘a spiritual power which protects and hovers over someone continuously, driving from him anything harmful which may happen to approach his body and soul. This is something which is perceived  invisibly by the illumined intellect that has knowledge by means of the eye of faith...’[8] Thus, both the first and the second overshadowing have a mystical character, but the second is accompanied by the ‘invisible vision’, that is, the experience of contemplation of the invisible reality which is accessible for the ‘illumined intellect’. Overshadowing is therefore semantically close to the terms ‘vision’ and ‘contemplation’.

            The term nahhiruta, ‘illumination’, also refers to the influence of divine grace over a person: it derives from nuhra, ‘light’, and points to such an action of God within a person which is accompanied by the presence of light. Isaac develops the theme of illumination in Chapter VI of Part II: 

When, through the grace and mercy of our Lord Jesus Christ, that illumination of mind of which the Fathers speak has begun to shine out in you, there are two signs which will give you confirmation concerning this... Now one of the signs is this: once this hidden light starts shining in your soul you will have the sign, that whenever you leave off the reading Scripture or prayer, the mind will be caught up with certain verses or with the content of these, and it will mediate on, examine and probe of its own accord into their spiritual significance; it will be so bound up with them that it will not depart from them and be distracted by anything else in creation... The second sign, which is as precise as the first, is the following: when the soul leaves the darkness and becomes light from within, then prolonged kneelings are granted to the solitary, and tarrying in them will prove so delightful that he may be three days kneeling on the ground in prayer, without his knowing any fatigue as a result of the delight... and his heart becomes silent. In this way a delightful stillness takes hold of his heart and his limbs to such an extent that he does not even conceive, one might say, of the Kingdom of heaven as being comparable in its delightfulness to this stillness in prayer...[9] 

            In this passage, the question is of an illumination such that happens in a somewhat leisurely and invisible manner, and is recognized by external signs rather than by internal feeling. Isaac clearly points to the nature of the light of which he speaks: it is ‘the light of the soul’, or ‘the soul which becomes light’. The illumination consists in that the soul goes out of darkness and begins to see its own natural light.

            It should be noted that the term ‘light’ (nuhra) is frequently encountered in Isaac’s writings, but the question is usually not of a certain visible and concrete light; neither is it of the divine light which is seen by mystics. The experience of vision of the divine light, of which both Syriac and Byzantine mystical writers spoke (John of Dalyatha, Symeon the New Theologian, Gregory Palamas and many others), if it was known to Isaac, was never described by him in detail. In this sense Isaac cannot be considered as a predecessor of Byzantine Hesychasm. Our statement may seem strange to those accustomed to the Greek text of Isaac or translations from it: they will immediately remember ‘the light of the Holy Trinity’, which shines, like the sun, in a person’s soul, ‘contemplation of the Holy Trinity’ and other similar phrases. However, none of them occur in authentic writings by Isaac, but either in the writings of John of Dalyatha and Philoxenus of Mabbug which were attributed to him, or in Isaac’s quotations from Evagrius.

            As regards authentic texts, whenever the phase ‘divine light’ (nuhra alahaya) occurs,[10] it does not have that specific and concrete character which it receives in Hesychast literature. The same should be affirmed concerning the phrases ‘the light of theoria’,[11] ‘the holy light’,[12] and the like. All of these expressions definitely refer to a certain inward experience of spiritual vision, but it is a question here of the vision by an ascetic of the light of his own soul as a result of illumination from above which has taken place in his intellect. This is the content of the passage on illumination quoted above. The notion of the natural light of the human soul is known to Evagrius: he speaks of such a state when the ‘inner man’, who became a ‘gnostic’, contemplates ‘the light of the beauty of his soul’.[13] Evagrius distinguished between the divine light, which is the light of the Holy Trinity, and the natural light of the human soul, which is contemplated by ascetics during prayer. Isaac did quote Evagrius’ texts concerning the vision of the light of the Holy Trinity, but in his own writings he spoke more regularly of the inner and hidden light of the human soul.

            The sources of spiritual illumination and of the radiance of the light inside one’s soul are prayer and other ascetical activities. Reflection ‘on the ministry of righteousness’, is also a source of spiritual illumination.[14] Among other sources of illumination and overshadowing, there are the memory of God and night vigil: ‘Good soil which gladdens its husbandman by bringing forth fruit an hundredfold is a soul that is made radiant by the remembrance of God and unsleeping vigil both day and night. The Lord establishes on her steadfastness a cloud that overshadows her by day and with a flaming light He illumines her by night: within her darkness a light shines’.[15] Finally, kneelings with contrition may also contribute to one’s inner illumination: ‘At whatever time God should open up your thinking from within, give yourself over to unremitting bows and prostrations... Then light will dawn within you, and your righteousness will quickly shine forth, and you will be like a paradise of burgeoning flowers and an unfailing fountain of waters’.[16]

            The radiance of the light in one’s soul is a source of constant spiritual joy: ‘Until someone loses the faith which is in his heart - by this I mean the certain knowledge of this divine care which will prevent him from falling into darkness of mind, from which comes anxiety and anguish - for otherwise his soul is filled all the time with light and joy, and it exults continually - that person dwells as though in heaven in the illumination of his thoughts which the faith of his heart instills in him; and from this point on he is also held worthy of the revelation of insights’.[17]

            The theme of spiritual joy brings us to a discussion of mystical ‘wonder’, another important feature of Isaac’s mysticism.