The mind of a heedful man is as it were a watchman on duty, or an unsleeping guard of the inner Jerusalem. Standing at the height of spiritual contemplation, he looks with an eye of purity upon the enemy powers who go around and attack his soul, in accordance with the Psalmist: 'And my eye hath looked down upon my enemies' (Ps. 53:9). From his eye the devil is not hidden, who 'as a roaring lion walketh about seeking whom he may devour' (I Pet. 5:8), nor are they who bend their bow 'to shoot in the dark the upright of heart (Ps. 10:2). And thus such a man, following the teaching of the divine Paul, receives 'the whole armor of God, that [he] may be able to withstand in the evil day (Eph. 6:13), and with this armor and with the cooperating grace of God, he repels visible attacks and vanquishes invisible warriors.
-St. Seraphim of Sarov, Spiritual Instructions no. 30, Little Russian Philokalia Vol. 1; Saint Herman of Alaska Brotherhood pgs. 48-49, 19th century


How could the human race go to God if God had not come to us? How should we free ourselves from our birth into death if we had not been born again according to faith by a new birth generously given by God, thanks to that which came about from the Virgin's womb?
-Irenaeus of Lyons, Against Heresies, IV, 33,4, Sources Chretiennes, Cerf, Paris found in The Roots of Christian Mysticism by Olivier Clement, p. 37., 130-208


Through their prayers for, and alms on behalf of, the deceased, Christians display the relationship between this world and the world to come.
The Church in this world and the Church in the other world are one and the same the one Body of Christ one the Church Militant and the other the Church Triumphant. It can be compared to a tree which has roots beneath the earth comprise as well as branches above the earth, but both the roots and the branches comprise one organism. This metaphor also illustrates how we on earth who comprise the Church Militant can receive help from the saints and the righteous ones in the Heavenly Church Triumphant. Saint Athanasios says: 'As it happens with wine inside a barrel which, when the vineyard blooms in the field, senses it and the wine itself blossoms together with it, so it is with the souls of sinners. They receive some relief from the Bloodless Sacrifice offered for them and from charity' performed for their repose.
Saint Ephrem the Syrian cites that same example with wine and the vineyard and concludes: 'And so, when there exists such mutual sensitivity even among plants, is not the prayer and sacrifice felt even more for the departed ones?'
'[At the Eucharist] the bread itself and the wine are changed into God's body and blood. But if you enquire how this happens, it is enough for you to learn that it was through the Holy Spirit, just as the Lord took on Himself flesh that subsisted in Him and was born of the Holy Mother of God through the Spirit. And we know nothing further save that the Word of God is true and energises and is omnipotent, but the manner of this cannot be searched out. But one can put it well thus, that just as in nature the bread by the eating and the wine by the drinking are changed into the body and blood of the eater and drinker, and do not become a different body from the former one, so the bread of the table and the wine and water are supernaturally changed by the invocation and presence of the Holy Spirit into the body and blood of Christ, and are not two but one and the same.'
-St. John of Damascus, An Exact Exposition of the Orthodox Faith, Book 4: Chapter 13; Eerdmans pg. 83, 8th century