Heinrich Müller on Little Sins
You only combat the great sins and do not want to be called a murderer, thief, or adulterer, so that you have no shame before the world. Meanwhile, little sins, which you do not observe, put your flesh to the test. You love the company of people, follow the example of their elegant, costly clothing, share with them a friendly joke about this or that thing, thereby being wounded in your heart, though you are not aware of the wounds. Your former zeal for Christianity decays gradually, dies away within you, until finally it happens that you die an eternal death from the wounds. See then how many great calamities arise more from little sins than from great ones. You consider great sins to be sins and avoid them, but you do not consider little sins to be sins and do not give them proper attention. I advise you to consider no sin little. However little they may appear, they offend God, wound your conscience, and become a root for many great sins.
from Spiritual Hours of Refreshment (1664), in Seventeenth Century Lutheran Meditations and Hymns, edited by Eric Lund (Paulist Press, 2011), 214.