St Gregory Palamas: Three Texts on Prayer and Purity of Heart
1. Because the Deity is goodness itself, true mercy and an abyss of loving bounty - or, rather. He is that which embraces and contains this abyss, since He transcends every name that is named (cf Eph. 1:21) and everything we can conceive - we can receive mercy only by union with Him. We unite ourselves to Him, in so far as this is possible, by participating in the godlike virtues and by entering into communion with Him through prayer and praise. Because the virtues are similitudes of God, to participate in them puts us in a fit state to receive the Deity, yet it does not actually unite us to Him. But prayer through its sacral and hieratic power actualizes our ascent to and union with the Deity, for it is a bond between noetic creatures and their Creator. Or at least this happens when our prayer, through its fervent compunction, transcends the passions and conceptual thoughts; for the intellect, while still passion-dominated, cannot be united to God. Thus so long as the intellect when praying remains in a passion- charged state, it will not obtain mercy; but to the extent that it can dispel distractive thoughts it will experience inward grief, and in so far as it experiences such grief it will partake of God's mercy. And if with humility it continues to savor this mercy it will transform entirely the aspect of the soul that is accessible to passion.
2. When the intellect's oneness becomes threefold, yet remains single, then it is united with the divine Triadic Unity, and it closes the door to every form of delusion and is raised above the flesh, the world and the prince of the world. As the intellect thus escapes the grip of these enemies, it finds itself in itself and in God; and for as long as it abides in this state it delights in the sense of spiritual jubilation that springs up within it. The intellect's oneness becomes threefold, yet remains single, when it reverts to itself and through itself ascends to God. The intellect's return to itself is its own self-guarding, while its ascent to God is initiated through prayer, prayer that is succinct, although at times it may be more lengthy in form, which requires more effort. If you persist in concentrating your intellect in this way and in raising it up towards the Deity, and in forcibly restraining the mind's propensity to stray hither and thither, you will draw noetically close to God. will reap things ineffable, taste the age to come, and by noetic perception will know that the Lord is fall of bounty, in accordance with the Psalmist's words, 'Taste and know that the Lord is bountiful' (Ps. 34:8). It is, perhaps, not very difficult for the intellect to find itself in the threefold state - for it itself to be, that is to say, both the guard, that which is guarded, and that which prays while it is keeping guard; but it is extremely difficult to persevere for a long time in this state that gives birth to things ineffable, for the effort involved in acquiring every other virtue is slight and altogether easy to sustain when compared with this. Hence many, unable to endure the self-constraint needed for acquiring the virtue of prayer, do not attain a plenitude of divine gifts; but those who do persist are rewarded with greater manifestations of divine aid, which sustain, support and joyfully carry them forward. Then what is difficult to accomplish is easily achieved, for they are invested with what one might call an angelic capacity, which empowers our human nature to commune with what lies beyond it. This accords with the words of the prophet, that those who persist will grow wings and will gain new strength (cf Isa. 40:31).
3. The intellectual activity consisting of thought and intuition is called intellect, and the power that activates thought and intuition is likewise the intellect; and this power Scripture also calls the heart. It is because the intellect is pre-eminent among our inner powers that our soul is deiform. In those devoted to prayer, and especially to the single-phrased Jesus Prayer, the intellect's noetic activity is easily ordered and purified; but the power that produces this activity cannot be purified unless all the soul's other powers are also purified. For the soul is a single entity possessing many powers. Thus if one of its powers is vitiated the whole of it is denied; for since the soul is single, the evil in one of its powers is communicated to alt the rest Now since each of the soul's powers produces a different energy, it is possible that with diligence one of these energies might be temporarily purified; but the power in question will not therefore be pure, since it communes with all the rest and so it remains impure rather than pure. Suppose, then. that a person has purified his intellectual energy through diligence in prayer, and has been to a certain extent enlightened either by the light of knowledge or in addition by noetic illumination: if he considers himself for this reason to be pure he deceives himself and is utterly mistaken, and through his presumption he throws wide open a door into himself for the devil, who always strives to delude us human beings. But if he recognizes his heart's impurity, and is not filled with pride because of the partial degree of purity he has attained, but uses it as an aid, then he will see more clearly the impurity of the other powers of his soul and will progress in humility, his inward grief will grow and he will find suitable ways of healing each of his soul's powers. He will cleanse its moral aspect with the right kind of ascetic practice, its power of spiritual apperception with spiritual knowledge, its power of contemplation with prayer, and in this way he will attain perfect, true and enduring purity of heart and intellect - a purity that no one can ever experience except through perfection in the ascetic life, persistent practice, contemplation and contemplative prayer.