The following quotation comes from Martin Luther’s treatise On Christian Liberty (pp. 5-7):

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 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.