Sayings of The Holy Fathers:

"And Abraham departed and lingered in the wilderness" (Gen. 12:9). The mind is tested when it is in the wilderness, where there is no lewdness of desires, no abundance of wealth, no excess of luxury. Would that I could be in the wilderness, bereft of every incentive of desires, forsaken by every wish to offend, stripped of the bombast of ostentation! But, either because God allows us to be tested or because the Tempter attacks us, when the mind seems to itself to be in the wilderness, at rest from all longing for earthly pleasures, it is driven into Egypt, where it can be goaded. For the goad of our mind is our flesh, and its passions ae our stings. This is our Egypt, namely, our flesh; this is our affliction.

St. Ambrose of Milan, On Abraham

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The brethren also asked Abba Agathon, "Amongst all good works, which is the virtue which requires the greatest effort?" He answered, "Forgive me, but I think there is no labor greater that that of prayer to God. For every time a man wants to pray, his enemies, the demons,want to prevent him, for they know that it is only by turning him from prayer that they can hinder his journey. Whatever good work a man undertakes, if he perseveres in it, he will attain rest. But prayer is warfare to the last breath.

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Fervent, tearful prayer not only cleanses from sins, but also cures bodily infirmities and maladies; it renews the whole of a man's being, and makes him, so to say, born again (I speak from experience), O what a priceless gift prayer is!

Glory to Thee, the Only-Begotten Son of God, Who hast obtained for us through Thy mediation the endless pardon of our sins! Glory to the All-Holy Spirit, Who 'maketh intercession for us with groanings which cannot be uttered" (Rom. 8:26) - who gives us ardent prayer with groanings and tears, Who warms our cold souls and gives contrition and sorrow for sins, cleansing, sanctifying, pacifying, strengthening, and renewing us!

Glory to Thee, Holy Trinity, Which has no beginning, Life-giving, eternally glorified by all rational creatures!

St. John of Kronstadt

My Life in Christ, Part 1, Holy Trinity Monastery pgs. 148-149