It is plain from St. Paul, that a spiritual person is one who has the Holy Spirit bearing witness in his heart and knows for sure that he is a dwelling-place of the Holy Triune God. Thus he understands clearly that he is a son of God by grace, and within his heart he cries out in the Holy Spirit, “Abba, Father”. According to the testimony of the Saints, this heartfelt cry is essentially noetic prayer or prayer of the heart.

St. Basil the Great, examining what it means for a person to become a temple of the All-Holy Spirit, teaches – inspired by God – that the man who is the temple of the Holy Spirit, is not disturbed by temptations and constant cares; he seeks God and has communion with Him. Clearly the spiritual man is he who has the Holy Spirit within and this is confirmed by his interrupted remembrance of God.

According to St. Gregory Palamas, just as the man endowed with reason is called rational, so someone who is rich in the Holy Spirit is called spiritual. Therefore, according to St. Gregory Palamas, the spiritual man is the ‘new man’, who has been regenerated by the grace of the Most Holy Spirit.

The same outlook is shared by all the holy Fathers. St. Symeon the New Theologian, for example, says that the man who is prudent, forbearing and meek, and who prays and beholds God, “walks in the Spirit”. He is pre-eminently the spiritual man, par excellence.

Again according to St. Symeon the New Theologian, when the noetic and rational parts of a man’s soul are not clothed in the image of Christ, he is considered a man of the flesh, since he does not have the sense of spiritual glory. Such a carnal person is like someone who is blind and unable to see the light of the sun. In fact he is considered both blind and lifeless. In contrast, the spiritual man, who partakes in the energies of the Holy Spirit, is alive in God.

Source: Orthodox Spirituality, by Metropolitan of Nafpaktos Hierotheos