He who will not accept a reproof, just or unjust, renounces his own salvation. But he who accepts it with an effort, or even without an effort, will soon receive the remission of his sins.

St. John Climacus

If we have not committed the sins that others have, perhaps this is because we did not have the opportunity – the situation and circumstances were different. In each person there is something good and something bad; we usually see only the vices in people and we see nothing that is good.

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

Until a man’s earthly life finishes its course, up to the very departure of the soul from the body, the struggle between sin and righteousness continues within him. However, high a spiritual and moral state one might achieve, a gradual or even headlong and deep fall into the abyss of sin is always possible. Therefore, communion of the holy Body and Blood of Christ, which strengthens our contact with Him and refreshes us with the living streams of the grace of the Holy Spirit flowing through the Body of the Church, is necessary for everyone.

St. John of Shanghai and San Francisco

We must consider all evil things, even the passions which war against us, to be not our own, but of our enemy the devil. This is very important. You can only conquer a passion when you do not consider it as part of you.

St. Nikon of Optina

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

When the soul of a man departs from the body, a certain great mystery is there enacted. If a person is under the guilt of sin, bands of demons and fallen angels approach along with the powers of darkness which capture the soul and drag it as a captive to their place. No one should be surprised by this fact. For if, while a man lived in this life, he was subject to them and was their obedient slave, how much more, when he leaves this world, is he captured and controlled by them?

St. Macarius the Great

Why do demons wish to excite in us gluttony, fornication, greed, anger, rancor and other passions? So that the mind, under their weight, should be unable to pray as it ought; for when the passions of our irrational part begin to act, they prevent the mind from acting rationally.

St. Nilus of Sinai

Not every "good" deed is actually good, but only that good deed which is done for the sake of God.  The externals of a particular action are not its essence; God alone sees a person's heart.  We need to humble ourselves, realizing that every good deed is mixed with some passion.

St. Nikon of Optina

The grace of the Holy Spirit which is given mystically to every Christian when he is baptized acts and is manifested in proportion to our obedience to the commandments of the Lord. That is, if a Christian obeys the commandments of the Lord more, grace acts with him more, while if he obeys them less, grace acts within him less. Just as a spark, when covered in the ashes of fire becomes increasingly manifest as one removes the ashes, and the more fire wood you put the more the fire burns, so the grace that has been given to every Christian through Holy Baptism is hidden in the heart and covered up by the passions and sins, and the more a man acts in accordance with the commandments of Christ, the more he is cleansed of the passions and the more the fire of Divine grace lights in his heart, illumines and deifies him.

St. Nicodemus of the Holy Mountain

We have within us deeply rooted weaknesses, passions, and defects. This can not all be cut out with one sharp motion, but patience, persistence, care and attention. The path leading to perfection is long. Pray to God so that he will strengthen you. Patiently accept your falls and, having stood up, immediately run to God, not remaining in that place where you have fallen. Do not despair if you keep falling into your old sins. Many of them are strong because they have received the force of habit. Only with the passage of time and with fervor will they be conquered. Don’t let anything deprive you of hope.

St. Nectarios of Aegina

And pray without ceasing in behalf of other men. For there is in them hope of repentance that they may attain to God. See, then, that they be instructed by your works, if in no other way. Be meek in response to their wrath, humble in opposition to their boasting: to their blasphemies return your prayers; in contrast to their error, be steadfast in the faith; and for their cruelty, manifest your gentleness.

St Ignatius of Antioch

It is required that not only with the body should we fast, but with the soul. Now the soul is humbled when it does not follow wicked opinions, but feeds on becoming virtues. For virtues and vices are the food of the soul, and it can eat either of these two. Bend your appetite toward virtues, as Paul says, "Being nourished by the word of truth."

St. Athanasios of Alexandria