Elder Ephraim of Philotheou: Talk only a little, and be watchful over thoughts

 Do not talk a lot. Stay away from back talk, quarreling, loquacity, and everything that issues from a careless tongue. Drive away evil thoughts and filthy fantasies from your mind as soon as they appear. For when the linger inside the mine and heart, they create a grave condition. Whereas when we are careful at the first appearance of the filthy fantasy and the filthy thought that follows, we remain in peace and enjoy the moral gratification of purity.

Therefore, my children, let us pay attention to ourselves every time various bad thoughts enter, because the same approach applies for every bad thought. Whatever kind is may be, when it finds the nous careless, it enters and creates - corresponding to the passion - the aforementioned unhealthy condition.

Therefore, since a monk is fought primarily by thoughts, the thing that saves him is watchfulness! Watchfulness (nepsis) is derived from the word "nēfo," that is, to be careful, vigilant, alert, and on our guard. When we are careful, vigilant, alert, and on our guard, the house of our soul will be well-kept and we shall save our souls for which we struggle our whole life.

+Elder Ephraim of Philotheou, from Counsels from the Holy Mountain, Chapter 14 On Thoughts Fantasies and Distractions, #9

St. Nikephorus the Monk: On What is Attention

 What is attention and what are its qualities - this you must diligently study. Attention is knowledge given by pure repentance; attention is the cry of the soul, the hatred of the world, the ascent to God. Attention is rejection of sin and acceptance of virtue. Attention is the undoubted conviction of the of the forgiveness of sins. Attention is the beginning of the vision of the mind, or rather, the cause of the vision of the mind, for God, through it, comes down and appears to the mind. Attention is the lack of confusion of the mind or, more properly, its firmness, given to the soul by God's mercy. Attention is the defeat of thoughts, the temple of the remembrance of God, the treasure-store of endurance when encountering dangers. Attention is the cause of faith, hope, and love.

+St. Nikephorus the Monk, from The Philokalia, volume 4 

Elder Ephraim of Philotheou: On Watchfulness

 Abba Paphnutios was a renowned desert father. One day as he was walking, he noticed two people committing a certain sin. A sinful though assailed him: "Look at the great evil they are doing!" He saw them with his own eyes and was immediately bombarded by this thought, which attempted to assault the saint's pure soul by pushing him either to criticize or to become scandalized. However, being practiced in watchfulness, he immediately perceived the assault and responded to himself, "They are sinning today; I will sin tomorrow. They will repent, but I am a hard-hearted, unrepentant, and prideful man. I will not repent, and I will end up in Hell. Truly, I am worse than these two people. I am full of passions; therefore, what can I say about these people who are less sinful than me?" By thinking this way, he brought the sinful invitation to a dead stop and avoided condemning the people who were transgressing.

He did not walk much further when an angel of God appeared before him, holding a double-edged sword dripping with blood. The angel asked him, "Paphnutios, do you see this sword? Do you see the blood that is dripping?"

"I see it, O angel of God."

"With this sword, I execute and behead them who judge their fellow man. Since you did not judge the two people who were indeed sinning - not just ones whom you suspected to be sinning, but whom you actually saw with your very own eyes - but condemned yourself instead, your name has been written in the book of eternal life."

+Elder Ephraim of Philotheou, from The Art of Salvation, homily 11 on Watchfulness, Prayer, and Confession

St. Paisius Velichkovsky: On Walking with Heedfulness

 Every evening we must test ourselves as to how the day passed with us, and every morning we again should test ourselves as to how the night passed. And not only at some definite time but at every time and in every place and concerning everything we must give account of ourselves, and reflect concerning everything we must give account to ourselves, and reflect concerning the virtues and the passions, in what condition of life we are: in the beginning, at the middle, or at the end: whether we are laboring worthy of the rewards and performing virtues, or only laboring without receiving rewards. When we sin in anything, let us make up for our lack of virtue by tears and let us weep. 

+St. Paisius Velichkovsky, from Field Flowers, or Lilies of the Field from the Divine Scripture, Concerning God's Commandments and the Holy Virtues, #18 On Walking with Heedfulness, in Little Russian Philokalia, Volume 4.