From the Imitation of Christ [Thomas à Kempis]:

When a man desires a thing too much, he at once becomes ill at ease. A proud and avaricious man never rests, whereas he who is poor and humble of heart lives in a world of peace. An unmortified man is quickly tempted and overcome in small, trifling evils; his spirit is weak, in a measure carnal and inclined to sensual things; he can hardly abstain from earthly desires. Hence it makes him sad to forego them; he is quick to anger if reproved. Yet if he satisfies his desires, remorse of conscience overwhelms him because he followed his passions and they did not lead to the peace he sought.

True peace of heart, then, is found in resisting passions, not in satisfying them. There is no peace in the carnal man, in the man given to vain attractions, but there is peace in the fervent and spiritual man.

When the right and opportune moment comes for speaking, say something that will edify.

Bad habits and indifference to spiritual progress do much to remove the guard from the tongue. Devout conversation on spiritual matters, on the contrary, is a great aid to spiritual progress, especially when persons of the same mind and spirit associate together in God.

We should enjoy much peace if we did not concern ourselves with what others say and do, for these are no concern of ours. How can a man who meddles in affairs not his own, who seeks strange distractions, and who is little or seldom inwardly recollected, live long in peace?

Blessed are the simple of heart for they shall enjoy peace in abundance.

Why were some of the saints so perfect and so given to contemplation? Because they tried to mortify entirely in themselves all earthly desires, and thus they were able to attach themselves to God with all their heart and freely to concentrate their innermost thoughts.
We are too occupied with our own whims and fancies, too taken up with passing things. Rarely do we completely conquer even one vice, and we are not inflamed with the desire to improve ourselves day by day; hence, we remain cold and indifferent. If we mortified our bodies perfectly and allowed no distractions to enter our minds, we could appreciate divine things and experience something of heavenly contemplation.

The greatest obstacle, indeed, the only obstacle, is that we are not free from passions and lusts, that we do not try to follow the perfect way of the saints. Thus when we encounter some slight difficulty, we are too easily dejected and turn to human consolations. If we tried, however, to stand as brave men in battle, the help of the Lord from heaven would surely sustain us. For He Who gives us the opportunity of fighting for victory, is ready to help those who carry on and trust in His Grace.

[resources: The Imitation of Christ, the Imitation of Saint Joseph, and Michael Brown retreat, April 15]