It is this war of attention and prayer on which both life and death of the soul depend. By attention that we keep our prayer safe and therefore we progress: if we do not have attention to keep it clear and we leave it unguarded, then it is inflected by evil thoughts and we become wicked and hopeless.

St. Symeon the New Theologian

Be concentrated without self-display, withdrawn into your heart. For the demons fear concentration as thieves fear dogs.

St. John Climacus

In going to church, think that you art going to the house of the King of Heaven, where with fear and joy one ought to stand as in heaven before the King of Heaven. While standing in church, do not look around to the sides and do not look at how someone is standing and praying, lest you be condemned with the Pharisee, since you did not come to judge others, but to ask for mercy for yourself from God the Judge and Knower of hearts. Gaze with compunction toward the altar alone, where the holy sacrifice is offered. More than anything else, beware of laughter and conversations, for whoever laughs or converses while standing in church does not render honor to the holy place and tempts others and prevents others from praying.

St. Tikhon of Zadonsk

Sinful thoughts continually disturb a man. But if he does not cooperate with them, then he is not guilty of them. 

St. Ambrose of Optina

Grumbling is caused by misery and it can be put aside by doxology (giving praise). Grumbling begets grumbling and doxology begets doxology. when someone doesn’t grumble over a problem troubling him, but rather praises God, then the devil gets frustrated and goes off to someone else who grumbles, in order to cause everything to go even worse for him. You see, the more one grumbles, the more one falls into ruin. 

Sometimes the devil deceives us and makes us unable to be pleased with anything; however, one can celebrate all things in a spiritual manner, with doxology, and secure God’s constant blessing.

St. Paisios of Mount Athos

Run from places of sin as from the plague. For when fruit is not present, we have no frequent desire to eat it.

St. John Climacus

Some people tell me that they are scandalized because they see many things wrong in the Church. I tell them that if you ask a fly, “Are there any flowers in this area?” it will say, “I don’t know about flowers, but over there in that heap of rubbish you can find all the filth you want.” And it will go on to list all the unclean things it has been to. 

Now, if you ask a honeybee, “Have you seen any unclean things in this area?” it will reply, “Unclean things? No, I have not seen any; the place here is full of the most fragrant flowers.” And it will go on to name all the flowers of the garden or the meadow. 

You see, the fly only knows where the unclean things are, while the honeybee knows where the beautiful iris or hyacinth is. As I have come to understand, some people resemble the honeybee and some resemble the fly. Those who resemble the fly seek to find evil in every circumstance and are preoccupied with it; they see no good anywhere. But those who resemble the honeybee only see the good in everything they see. 

The stupid person thinks stupidly and takes everything in the wrong way, whereas the person who has good thoughts, no matter what he sees, no matter what you tell him, maintains a positive and good thought.

St. Paisios of Mount Athos

No one and not one thing can bring harm to a person if he does not harm himself, and conversely, a thousand means and ways to salvation will not help the person who will not avoid sin.

St. Nikon of Optina

A Christian must be courteous to all. His words and deeds should breathe with the grace of the Holy Spirit, which abides in his soul, so that in this way he might glorify the name of God. He who regulates all of his speech also regulates all of his actions. He who keeps watch over the words he is about say also keeps watch over the deeds he intends to do, and he never goes out of the bounds good and benevolent conduct. The graceful speech of a Christian is characterized by delicateness and politeness. This fact, born of love, produces peace and joy. On the other hand, boorishness gives birth to hatred, enmity, affliction, competitiveness, disorder and wars.

St. Nectarios of Aegina

These eight passions should be destroyed as follows: gluttony by self-control; unchastity by desire for God and longing for the blessings held in store; avarice by compassion for the poor; anger by goodwill and love for all men; worldly dejection by spiritual joy; listlessness by patience, perseverance and offering thanks to God; self-esteem by doing good in secret and by praying constantly with a contrite heart; and pride by not judging or despising anyone in the manner of the boastful Pharisee (cf. Luke 18 : 11–12), and by considering oneself the least of all men. When the intellect has been freed in this way from the passions we have described and been raised up to God, it will henceforth live the life of blessedness, receiving the pledge of the Holy Spirit (cf. 2 Cor. 1 : 22). And when it departs this life, dispassionate and full of true knowledge, it will stand before the light of the Holy Trinity and with the divine angels will shine in glory through all eternity.

St John of Damascus 

If you have not yet received the gift of self-control, know that the Lord is ready to hear you if you entreat Him with prayer and hope.

St. John of Karpathos