From the Word
20 For no human being will be justified in his sight by works of the law, since through the law comes knowledge of sin. 21 But now the righteousness of God has been manifested apart from law, although the law and the prophets bear witness to it, 22 the righteousness of God through faith in Jesus Christ for all who believe. For there is no distinction; 23 since all have sinned and fall short of the glory of God, 24 they are justified by his grace as a gift, through the redemption which is in Christ Jesus
Romans 3:19–24, RSV
The law is known when I learn from it that I am a sinner and am condemned, and see that there is no hope nor comfort anywhere for me, and I cannot help myself, but must have another one to deliver me. Then is the time I look around for him who can help, and he is Christ Jesus, who for this purpose became man, like unto us, in order that he might help us out of the mire into which we have fallen. He loved God with all his heart and his neighbor as himself, and submitted his will to the will of his Father, fulfilled the law in every respect; this I could not do and yet I was required to do it. God accepts him; and that which he fulfilled in the law, he offers me. He freely gives me his life with all his works, so that I can appropriate them to myself as a possession that is my own and is bestowed upon me as a free gift.
Christ has through his death secured for us the Holy Spirit; he fulfils the law in us and not we. For that Spirit, whom God sends into your heart for the sake of his Son, makes an entirely new man out of you, who does with joy and love from the heart everything the law requires, which before would have been impossible for you to do. This new man submits himself wholly and entirely to the will of God. Whatever God does with him, is well pleasing to him. This Spirit you cannot merit yourself, but Christ has secured it. When I believe from the heart that Christ did this for me, I receive also the same Holy Spirit that makes me an entirely new man. Then everything God commands is sweet, lovely and agreeable, and I do what he desires of me; not by my own strength, but by the the strength of him that is in me, as Paul says, “I can do all things through Christ that strengtheneth me.”
But take heed that you do not undertake to secure this faith in Jesus Christ by your own works or power. The Holy Ghost must do it, and faith alone is sufficient to this end. Our good works are for another purpose, namely, to prove our faith.
Luther, Martin, and John Sander. Devotional Readings from Luther’s Works for Every Day of the Year. Augustana Book Concern, 1915, pp. 337–38.