“One thing, and only one thing, is necessary for Christian life, righteousness, and freedom. That one thing is the most holy Word of God, the gospel of Christ, as Christ says, John 11:25, “I am the resurrection and the life; he who believes in me, though he die, yet shall he live”; and John 8:36, “So if the Son makes you free, you will be free indeed”; and Matt. 4:4, “Man shall not live by bread alone, but by every word that proceeds from the mouth of God.”
Let us then consider it certain and firmly established that the soul can do without anything except the Word of God and that where the Word of God is missing there is no help at all for the soul.
If it has the Word of God it is rich and lacks nothing since it is the Word of life, truth, light, peace, righteousness, salvation, joy, liberty, wisdom, power, grace, glory, and of every incalculable blessing. This is why the prophet in the entire Psalm 119 and in many other places yearns and sighs for the Word of God and uses so many names to describe it.
On the other hand, there is no more terrible disaster with which the wrath of God can afflict men than a famine of the hearing of his Word, as he says in Amos 8:11. Likewise there is no greater mercy than when he sends forth his Word, as we read in Psalm 107:20: “He sent forth his word, and healed them, and delivered them from destruction.”
Nor was Christ sent into the world for any other ministry except that of the Word. Moreover, the entire spiritual estate—all the apostles, bishops, and priests—has been called and instituted only for the ministry of the Word.
You may ask, “What then is the Word of God, and how shall it be used, since there are so many words of God?”
I answer: The Apostle explains this in Romans 1. The Word is the gospel of God concerning his Son, who was made flesh, suffered, rose from the dead, and was glorified through the Spirit who sanctifies.
To preach Christ means to feed the soul, make it righteous, set it free, and save it, provided it believes the preaching. Faith alone is the saving and efficacious use of the Word of God, according to Rom. 10:9: “If you confess with your lips that Jesus is Lord and believe in your heart that God raised him from the dead, you will be saved.”
Furthermore, “Christ is the end of the law, that every one who has faith may be justified” (Rom. 10:4). Again, in Rom. 1:17, “He who through faith is righteous shall live.”
The Word of God cannot be received and cherished by any works whatever but only by faith. Therefore it is clear that, as the soul needs only the Word of God for its life and righteousness, so it is justified by faith alone and not any works; for if it could be justified by anything else, it would not need the Word, and consequently it would not need faith.”
–Martin Luther, The Freedom of the Christian (1520), in Luther’s Works, Vol. 31: Career of the Reformer I (ed. Jaroslav Jan Pelikan, Hilton C. Oswald, and Helmut T. Lehmann; vol. 31; Philadelphia: Fortress Press, 1999), 31: 345–346.