Along with Saint Ephrem who lived in the 4th century before the time that the Syriac-speaking Church was overcome by Hellenization, Saint Isaac of Nineveh, who lived in the 7th century is one of the greatest Syriac Fathers and stands in the same eastern mystical tradition who put great emphasis on the work of the Holy Spirit in God’s "economy" (oikonomia) of salvation. Saint Isaac of Nineveh lived though in the 7th century and being influenced both by Evagrius and Macarius, Isaac of Nineveh is quite “Greek” already. He was connected with the trend broadly known as “Messalianism” which rejecting the sacramental life practiced asceticism, poverty, celibacy, fasting, considering that the spiritual power was acquired by constant prayer that led to the indwelling by the Holy Spirit. Through intense meditation and non-sleep they pretended to see demons and God with their own physical eyes, a theological view anathematized by the Ecumenical Council of Ephesus.

But Saint Isaac was a saintly ascetic and at soul and by vocation a mystical poet and to judge him rigidly only by the canon and dogma may be somehow misleading inasmuch as when he was writing in a poetic manner or on spiritual, experiential thematic he went beyond the theological terminology, symbols and doctrine and even chose to formulate his thought not in a systematic or dogmatic way. As a profound mystic also he already entered in that light in which the symbols and types are melted in a fluid and living reality, beyond abstract theology or philosophy. He preferred to express this new reality by the way of moral exhortation and by observing the ontological states of changes in man affected by the power and the grace of the Holy Spirit. He has given to us that the real picture of a human life which receiving that light of the Spirit of God and passing through struggle and agony finally enters into the supernatural realm of divine joy.

Thus, to remain a branch in the spiritual tree of life the man needs this fundamental transformation towards peace, harmony, and equilibrium. This is a state in which the human being receives the grace to communicate in the mystery of God and the chance to be himself a whole person, a true man. In the 73-th Discourse, Saint Isaac wrote that it is the wisdom which comes from the Holy Spirit and brings in the soul the fruits of silence and peace, whereas the wisdom which comes from man is the source of destruction. It is the Spirit of God, which is sanctifying and uniting all.

Saint Isaac is a Nestorian by formation and belonging and even was sometimes called “the Nestorian of Nineveh”. But if in reality the Nestorianism was more a “verbal heresy”, we should recognize that Isaac’s inclination and approach to that peace of man with and in God through the spiritual experience of “heschasm” is the best proof of the saint’s exoneration and of his Orthodox faith and claim. In reality, Saint Isaac of Nineveh is one of the most profound and genuine representatives of the Christian Syriac mysticism, although the Muslims too recognize him as one of their first mystics.

He lived as a solitary monk and even during his sleep he was overwhelmed by mystical ecstasy in God. Like any mystic, he was dependent on congenial spirits and had aversion to dogmatic disputes. He was even against the reading books for such sources are in the genre the causes of schisms, accentuates the divisions between religious confessions and brings in the mind of the reader a spirit of slander which almost always turns against the peace of own soul. In this respect, for the mystic the dogmatic can be a barrier which may impede the man to ascend unto the One and All through the love for mankind. With such understanding he even interprets the Bible and the dogma of Christianity in an allegorical way. His mysticism is monistic in its view of the world and of God; moreover the only real Being is God. Satan is just a deviation of the will from the truth, but does not exist as a natural being.

Saint Isaac also acknowledges the Hellenistic idea that the power which is governing the world is the Providence and therefore is not an accident in whatever is happening to man, good or bad. This “Providence of grace” comes to man before the man’s self-purification and in this case it is “for its own sake”. Otherwise, it can grow in man so that it may “ascend the spiritual tower”. And if such good is done to us, we should acknowledge that the mediators concerning it “have been baptism and faith, by which thou art called in Jesus Christ unto good works; to whom and to the Father and to the Holy Ghost belong praise, honor and adoration, now and always and forever. Amen.”

All the Christian spiritual gifts come from the Father through the Son by the Holy Spirit: “All beautiful deeds and excellent distinctions which are seen in the soul, and the amazing stages which are administrated in the Church of Christ, are accomplished by the influence of the power of the Holy Ghost… The Ghost will level ways in our heart leading to faith. And by faith we shall gather provisions for this our true world.”

According to Isaac the Syrian, God gives this grace of the Holy Spirit only to the elect ones, these very few ones which have arrived to the merits to accomplish by themselves that unusual “integrity of the soul”. This grace of the Holy Spirit bestowed upon this kind of man caught in persevering prayers and vigil, enters through the doors of the integral soul in that side of man’s spirituality and like an abundant light is flooding the intellect which from this point is taught and guided by the Holy Spirit. The man’s thinking is becoming by now a pure thinking and his mind the light of consciousness. Through this channel the man receives the gift of faith and the fruit of knowledge through love. However, such a faith is not yet the revelation of the Christian Truth, but only the departure to that possibility of spiritual life through which the man can only contemplate the True God.

Isaac the Syrian acknowledges himself that he does not speak here of the creed of faith which makes a distinction between the Persons of God, the divine nature and the properties of each of the Persons in what he calls “the admirable "economy (oikonomia)”  of God. He speaks rather of that faith “which is the spiritual light that shines in the soul by grace.”  In this state of grace “the density of the body is then abolished and the vision becomes spiritual.” The intellect of man is absorbed by the spirit and guided towards God “by the vision of his ineffable glory”. In his Spiritual Treatise, Saint Isaac also acknowledges “I do not call this faith that a man believes in the discrimination of the adorable hypostasis of the Essence, or in the properties of His nature, or in the amazing government regarding humanity consisting in His accepting our nature. But I call this faith: the intelligible light which by grace downs in the soul and, without leaving room for doubt, supports the heart by the testimony of the mind, namely by the persuasion of hope which is far from all presumptions and not by tradition from hearsay. This light will show the spiritual eyes of the soul the hidden mysteries which are in the soul, and the secret riches of divinity which are concealed from the eyes of fleshly men and are revealed spiritually to those who at the table of Christ are brought up in meditation upon His laws… Thus, He will show man the holy power, which surrounds him at all times. That power is the Comforter.” According to Saint Isaac, the Comforter, Holy Ghost has an “intelligible influence” and constitute “the delight of the saints in the world… who possess Grace as their guide, while their eyes are full of tears, and with prayer and weeping they convert night into day…”.

Trying to explain the action of God through the Holy Spirit, Saint Isaac came to the conclusion that God is granting help to man in two ways: one symbolical-intelligible and the other practical. The first way is understood as the holiness which is received through the divine grace, namely, “by the influence of the Holy Ghost a man is made holy in body and soul, as in the cases of Elisha and John and Mary the blessed among women”. This kind of participation is beyond what happens to the common creature. Therefore, the man at “the rank and file of creatures” is helped by the Holy Spirit in a more practical manner, for this man is “to come to that practical holiness which is granted unto the other saints, in the revelation between the limbs and the body.” But to be “snatch away in ecstasy” by the divine revelation this man must situate himself above “the emotions of physic deliberation, on account of his communion with the Holy Ghost”. For it is that that exceeding power and greatness of the Holy Spirit is given only to those who believe. This does not mean that those guided by the Holy Spirit should neglect to struggle life-long for their salvation: “For the will of the Spirit is not to accustom those in whom it dwells to laziness and to invite them to comfort, but to labors and greater trouble.”

God who fashioned man in His likeness and made the worlds with His hand, has given us also “the revelation of His spirit” so that we … “sought to know and understand through the Spirit the divine nature”. The Holy Ghost also “joins with the things which man prays in some unattainable insights, which it stirs in him in accordance with his attitude of being moved so that by these insights the emotion of prayer ceases, the mind is absorbed in ecstasy and the desired object of prayer is forgotten.” Prayer is “steadfastness of mind which is transmitted only by the light of the Holy Trinity through ecstasy.” For it is that the Holy Spirit joins to things truth everything can become a kind of ecstasy without life. For it is that only when we realize the Spirit of Truth, the Comforter is praying without ceasing in us, that we clad with Christ.

The person who has ascended to this point of communion with God has already recovered the integrity of his nature, the most necessary condition to contemplate God in His uncreated Light. Only at this stage it is possible for man to experience the pure prayer which is provoked by the natural movement of our soul but becomes a permanent state of being by the grace of the Holy Spirit, the Paraclete which has made the body of man His Living Temple. This is called by Saint Isaac “the spiritual stage of man”. It may be said that this practice of pure prayer as it is described by Saint Isaac of Nineveh is very close with what we call the Byzantine “hesychasm”, rest or contemplation: “When the Spirit establishes his dwelling in man, the later can no longer stop praying for the Spirit never ceases praying in him”.

However, at this point Saint Isaac seems to be influenced more by the stoic concept of “apathy” and Greek providential thought. According to him the nature and freedom of man are suppressed by the action of the Holy Spirit, which takes control over man up to the point where man’s intellect enters a state of passivity: “When the action of Spirit seizes the intellect which orders the senses and the thoughts, the liberty of nature is suppressed; it does not govern anymore, it is governed…”

Such idea, as “the apathy”, was always considered by the Syriac Fathers as being essentially Christian. In fact, Saint Isaac was borrowing from Philo and Neo-Platonists the principle according to whom God’s spirit does not dwell in man, unless that man is purified from affections by the way of “apathy”. Saint Isaac agrees with the idea that the body of man is oppressed by the Spirit of God until the body dies making the sins to die also. Otherwise, we cannot ripe the harvest of spiritual fruits in whom the Spirit of God takes spiritual fruits in whom the Spirit of God takes pleasure also. So, to make possible our true repentance, purification and perfection we should fast, pray and mortify our body until our soul will become spiritually strong. The man can achieve in this way “the spiritual senses of the mind” and “the spiritual senses of the soul”, so that by a continual illumination the mirror of his spirit may become a reflection of the divine.

According to Saint Isaac the kingdom of God is quite as this “spiritual contemplation”, “spiritual knowledge” and “communion with God”. In a way such mysticism seems to be pantheistic color and is mainly concerned with the raising up of the level of purification and illumination rather than to be an attempt towards perfection and unity in the Body of Christ: “As the saints, in the world to come, do not pray, when the mind has been engulfed by the divine Spirit, but dwell in ecstasy in that delightful glory, so the mind, when it has been made worthy of perceiving the future blessings, will forget itself and all that it is here …” or “Now when the intellect withdraws itself from this and is exalted unto the unique Essence, by the contemplation of the properties of that good Nature, when the intellect descends again from that place and returns again to the worlds and their distinctions…”.

Hereby, Saint Isaac alike Evagrius has identified the gnosis of the Holy Trinity with the Kingdom of God. When Saint Isaac sustains that the man can have access to the true theology by the way of praxis, he in fact acknowledges some ideas taken from Origenist metaphysics, messalianism, neo-platonic and pelagian thought. Saint Isaac considers that the Holy Spirit which sanctifies the Bread and the Wine in the Eucharist is the same with the light which poured upon our soul and body when we pray. According to him also, the Church is the one who preserves and bears the mystery of the Holy Spirit, especially through that fire which is burning in the hearts of the Apostles, martyrs and Fathers of the Church. The Church is like the new ark of covenant through which the new people of God have passed over the waters of baptism to find the Father and the Son and the Holy Spirit on that mysterious land of promises.

In spite of many contradictions due partially to the fact that Saint Isaac’s theological thinking was lacking a good discipline, his spiritual writings are the fruits of mystical and personal experience rather that an act of academic erudition. To use one of his expressions, his works were written with blood, not with ink. For this reason Saint Isaac of Nineveh is considered by the Orthodox Church as one of her ascetically and spiritual saints in the line of Saint John Climacus. In his spiritual growth and search after God, Saint Isaac was partially influenced by the writings of Saint Basil, Dyonis of Areopagite, Theodore of Mosuestia, Eprhem the Syrian, and especially Saint Macarius and Evagrius of Ponticus. His thought was formed in the mystical School of Nestorius and through Saint Isaac of Nineveh a new and particular way of Christian living and thinking came into a tradition which will give the saints as Saint Symeon the New Theologian and Maximus the Confessor and great Christian thinkers as Arseniev and Khomiakov. Although neither Saint Isaac of Nineveh nor Saint Ephrem or the Syriac Church developed a sound theological doctrine of the Holy Spirit, they both and as whole produced great fruits of the Spirit.