An excerpt of a letter Luther wrote to George Spenlein, a fellow Augustinian Friar, on April 8 1516 – 18 months before posting his Ninety-five Theses:
‘Now I should like to know whether your soul, tired of its own righteousness, is learning to be revived by and to trust in the righteousness of Christ. For in our age the temptation to presumption besets many, especially those who try with all their might to be just and good without knowing the righteousness of God, which is most bountifully and freely given us in Christ. They try to do good of themselves in order that they might stand before God clothed in their own virtues and merits. But this is impossible. While you were here, you were one who held this opinion, or rather, error. So was I, and I am still fighting against the error without having conquered it as yet.
Therefore, my dear Friar, learn Christ and him crucified. Learn to praise him and, despairing of yourself, say, “Lord Jesus, you are my righteousness, just as I am your sin. You have taken upon yourself what is mine and have given to me what is yours. You have taken upon yourself what you were not and have given to me what I was not.” Beware of aspiring to such purity that you will not wish to be looked upon as a sinner, or to be one. For Christ dwells only in sinners. On this account he descended from heaven, where he dwelt among the righteous, to dwell among sinners. Meditate on this love of his and you will see his sweet consolation. For why was it necessary for him to die if we can obtain a good conscience by our works and afflictions? Accordingly you will find peace only in him and only when you despair of yourself and your own works. Besides, you will learn from him that just as he has received you, so he has made your sins his own and has made his righteousness yours…’