Thomas a Kempis, The Imitation of Christ 2.6

Of the joy of a good conscience

1. The testimony of a good conscience is the glory of a good man. Have a good conscience and you shall ever have joy. A good conscience is able to bear exceedingly much, and is exceedingly joyful in the midst of adversities; an evil conscience is ever fearful and unquiet.You shall rest sweetly if your heart condemns you not. Never rejoice unless when you have done well. The wicked have never true joy, nor feel internal peace, for there is no peace, says my God, to the wicked. And if they say "we are in peace, there shall no harm happen unto us, and who shall dare to do us hurt?" believe them not, for suddenly shall the wrath of God rise up against them, and their deeds shall be brought to nothing, and their thoughts shall perish.

2. To glory in tribulation is not grievous to him who loves; for such glorying is glorying in the Cross of Christ. Brief is the glory which is given and received of men. Sadness always goes hand in hand with the glory of the world. The glory of the good is in their conscience, and not in the report of men. The joy of the upright is from God and in God, and their joy is in the truth. He who desires true and eternal glory cares not for that which is temporal; and he who seeks temporal glory, or who despises it from his heart, is proved to bear little love for that which is heavenly. He who cares for neither praises nor reproaches has great tranquillity of heart.

3. He will easily be contented and filled with peace, whose conscience is pure.You are none the holier if you are praised, nor the viler if you are reproached.You are what you are; and you cannot be better than God pronounces you to be. If you consider well what you are inwardly, you will not care what men will say to you. Man looks on the outward appearance, but the Lord looks on the heart; man looks on the deed, but God considers the intent. It is the token of a humble spirit always to do well, and to set little by oneself. Not to look for consolation from any created thing is a sign of great purity and inward faithfulness.

4. He that seeks no outward witness on his own behalf, shows plainly that he has committed himself wholly to God. For not he that commends himself is approved, as St. Paul says, but whom the Lord commends. To walk inwardly with God, and not to be held by any outer affections, is the state of a spiritual man.