St. John Cassian (commentary on 1 Cor. 15:10):
When he says ‘I labored,’ he shows the effort of his own will; when he says yet not I, but the grace of God, he points out the value of the Divine protection; when he says with me, he affirms that grace cooperates with him when he is not idle or careless, but working and making an effort. (Conferences, XIII, 13)
…in all these (Scriptural quotations) there is a declaration both of the grace of God and the freedom of our will, because even of his own activity a man can be led to the quest of virtue, but always stands in need of the help of the Lord. (Conferences, XIII, 9)
For these two, that is, both grace and free will, seem indeed to be contrary to each other; but both are in harmony. And we conclude that, because of piety, we should accept both, lest taking on of these away from man, we appear to violate the Church’s rule of faith (Conferences, XIII, 11)
St. Maximos the Confessor:
“The divine Logos of God the Father is mystically present in each of His commandments….Thus, he who receives a divine commandment and carries it out receives the Logos of God who is in it; and he who receives the Logos through the commandments also receives through Him the Father who is by nature present in Him, and the Spirit who likewise is by nature in Him. ‘I tell you truly, he that receives whomever I send receives Me; and he that receives Me receives Him that sent Me’ (John 13:20). In this way, he who receives a commandment and carries it out receives mystically the Holy Trinity.”
St. Seraphim of Sarov:
“Prayer, fasting, vigil and all other Christian activities, however good they may be in themselves, do not constitute the aim of our Christian life, although they serve as the indispensable means of reaching this end. The true aim of our Christian life consists in the acquisition of the Holy Spirit of God. As for fasts, and vigils, and prayer, and almsgiving, and every good deed done for Christ’s sake, they are only means of acquiring the Holy Spirit of God. But mark, my son, only the good deed done for Christ’s sake brings us the fruits of the Holy Spirit. All that is not done for Christ’s sake, even though it be good, brings neither reward in the future life nor the grace of God in this.
“As we see from the sacred narrative, the man who works righteousness is so pleasing to God that the Angel of the Lord appeared at the hour of prayer to Cornelius, the God-fearing and righteous centurion, and said: ‘Send to Joppa to Simon the Tanner; there shalt thou find Peter and he will tell thee the words of eternal life, whereby thou shalt be saved and all thy house.’ Thus the Lord uses all His divine means to give such a man in return for his good works the opportunity not to lose his reward in the future life. But to this end we must begin here with a right faith in our Lord Jesus Christ, the Son of God, Who came into the world to save sinners and Who, through our acquiring for ourselves the grace of the Holy Spirit, brings into our hearts the Kingdom of God and opens the way for us to win the blessings of the future life.
“That’s it, your Godliness . In acquiring this Spirit of God consists the true aim of our Christian life, while prayer, vigil, fasting, almsgiving and other good works  done for Christ’s sake are merely means for acquiring the Spirit of God.”
“In the parable of the wise and foolish virgins, when the foolish ones lacked oil, it was said: ‘Go and buy in the market.’ But when they had bought, the door of the bride-chamber was already shut and they could not get in….I think that what they were lacking was the grace of the All-Holy Spirit of God. These virgins practiced the virtues, but in their spiritual ignorance they supposed that the Christian life consisted merely in doing good works. By doing a good deed they thought they were doing the work of God, but they little cared whether they acquired thereby the grace of God’s Spirit.”
“Of course, every good deed done for Christ’s sake gives us the grace of the Holy Spirit, but prayer gives us it most of all, for it is always at hand, so to speak, as an instrument for acquiring the grace of the Spirit….Acquire the grace of the Holy Spirit also by practicing all the other virtues for Christ’s sake.”
“And if we were never to sin after our Baptism, we should remain for ever Saints of God, holy, blameless and free from all impurity of body and spirit. But the trouble is that we increase in stature, but do not increase in grace and in the knowledge of God as our Lord Jesus Christ increased; but on the contrary, we gradually become more and more depraved and lose the grace of the All-Holy Spirit of God and become sinful in various degrees, and most sinful people. But if a man is stirred by the wisdom of God which seeks our salvation and embraces everything, and he is resolved for its sake to devote the early hours to God and to watch in order to find his eternal salvation , then, in obedience to its voice, he must hasten to offer true repentance for all his sins and must practice the virtues which are opposite to the sins committed. Then through the virtues practiced for Christ’s sake he will acquire the Holy Spirit Who acts within us and establishes in us the Kingdom of God. The word of God does not say in vain: The Kingdom of God is within you (Lk. 17:21), and it suffers violence, and the violent take it by force (Mat. 11:12) . That means that people who, in spite of the bonds of sin which fetter them and (by their violence and by inciting them to new sins) prevent them from coming to Him, our Saviour, with perfect repentance for reckoning with Him, yet force themselves to break their bonds, despising all the strength of the fetters of sin—such people at last actually appear before the face of God made whiter than snow by His grace. Come, says the Lord: Though your sins be as purple, I will make them white as snow (Is. 1:18).
The grace of the Holy Spirit is the light which enlightens man. The whole of Sacred Scripture speaks about this. Thus our holy Father David said: Thy word is a lamp to my feet, and a light to my path (Ps. 118:105)…. And in fact the Lord has frequently demonstrated before many witnesses how the grace of the Holy Spirit acts on people whom He has sanctified and illumined by His great inspiration . Remember Moses after his talk with God on Mount Sinai. He so shone with an extraordinary light that people were unable to look at him. He was even forced to wear a veil when he appeared in public. Remember the Transfiguration of the Lord on Mount Tabor. A great light encircled Him, and His raiment became shining, exceedingly white like snow (Mk. 9:3), and His disciples fell on their faces from fear. But when Moses and Elias appeared to Him in that light, a cloud overshadowed them in order to hide the radiance of the light of the divine grace which blinded the eyes of the disciples. Thus the grace of the All-Holy Spirit of God appears in an ineffable light to all to whom God reveals its action.
 As quoted in “The Place of Blessed Augustine in the Orthodoxy Church,” Fr. Seraphim Rose, St. Herman Press, 2007, p. 37.
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