Thomas á Kempis. The imitation of Christ. Book 2, chapter 3.

Of the good, peaceable person

First keep peace with yourself; then you will be able to bring peace to others. A peaceful person does more good than a learned one. A passionate person turns even good to evil and is quick to believe evil, but the peaceful person, being good themself, turns all things to good.

Whoever is at perfect ease is never suspicious, but the disturbed and discontented spirit is upset by many a suspicion, neither resting nor permitting others to rest. Such a one often says what ought not to be said and leaves undone what ought to be done—concerned with the duties of others but neglecting their own.

Direct your zeal, therefore, first upon yourself; then you may with justice exercise it upon those about you. You are well versed in colouring your own actions with excuses which you will not accept from others, though it would be more just to accuse yourself and excuse your brother or sister. If you wish others to bear with you, you must bear with them. Behold, how far you are from true charity and humility which does not know how to be angry with anyone, or to be indignant save only against self!

It is no great thing to associate with the good and gentle, for such association is naturally pleasing. Everyone enjoys a peaceful life and prefers persons of congenial habits. But to be able to live at peace with harsh and perverse people, or with the undisciplined and those who irritate us, is a great grace, a praiseworthy and manly thing.

Some people live at peace with themselves and with their fellows, but others are never at peace with themselves nor do they bring it to anyone else. These latter are a burden to everyone, but they are more of a burden to themselves. A few, finally, live at peace with themselves and try to restore it to others.