“Christ is completely wrapped in the Scriptures, just as the babe is wrapped in swaddling clothes. Preaching is the manger in which he lies and is apprehended, and from which we take our food.” (Sermon on Luke 2)
Preaching as God's own Word
“Tis a right excellent thing, that every honest pastor’s and preacher’s mouth is Christ’s mouth, and his word and forgiveness is Christ’s word and forgiveness… For the office is not the pastor’s or preacher’s but God’s; and the Word which he preacheth is likewise not the pastor’s and preacher’s but God’s." (Quoted in Church Dogmatics I/1, p107)
“[God] condescends to enter the mouth of every Christian who professes the faith.” [Therefore preaching must be] “believed as though God’s own voice were resounding from heaven” (LW24, 66)
"We both - pastor and listener - are only pupils; there is only this difference, that God is speaking to you through me. That is the glorious power of the divine Word, through which God Himself deals with us and speaks to us, and in which we hear God Himself." (LW 23, 97)
Therefore Preachers Inherit the Ministry of the Keys (Matthew 16:19)
[Jesus says,] “Peter’s mouth is my mouth, and his tongue is my key case. His office is my office, his binding and loosing are my binding and loosing. His keys are my keys, and I have no others, nor do I know of any others.” (LW40, 365)
“God has no other way to forgive sins than through the spoken Word, as he commanded us. [For] if you do not look for forgiveness through the Word, you will gape toward heaven in vain for grace, or (as they say), for a sense of inner forgiveness.” (LW40, 366]
Preaching Law and Gospel
“The law uncovers sin; it makes the sinner guilty and sick; indeed, it proves him to be under condemnation... The gospel offers grace and forgives sin; it cures the sickness and leads to salvation." (Romans Commentary)
Preaching the Gospels
"I believe that it has now become clear that it is not enough or in any sense Christian to preach the works, life, and words of Christ as historical facts, as if the knowledge of these would suffice for the conduct of life; yet this is the fashion among those who must today be regarded as our best preachers. Far less is it sufficient or Christian to say nothing at all about Christ and to teach instead the laws of men and the decrees of the fathers....Rather ought Christ to be preached to the end that faith in him may be established, that he may not only be Christ, but be Christ for you and me, and that what is said of him and is denoted in his name may be effectual in us. Such faith is produced and preserved in us by preaching why Christ came, what he brought and bestowed, what benefit it is to us to accept him." (The Freedom of the Christian, LW 31.357)
“The chief article and foundation of the gospel is that before you take Christ as an example, you accept and recognize him as a gift, as a present that God has given you and that is your own. This means that when you see or hear of Christ doing or suffering something, you do not doubt that Christ himself, with his deeds and suffering, belongs to you. On this you may depend as surely as if you had done it yourself; indeed as if you were Christ himself." (What to Look for and Expect in the Gospels)
The Nature of Preaching
"Preaching is naught other but an offering and presentation of Christ." Luther (LW39, 183)
“The preaching of the gospel is nothing else than Christ coming to us, or we being brought to him” (LW 35.121).
The Necessity of Preaching
“Even if Christ were given for us and crucified a thousand times it would all be vain if the Word of God were absent and were not distributed and given to me with the bidding, this is for you, take what is yours.” (LW 40, 213)
"To preach Christ means to feed the soul, make it righteous, set it free, and save it, provided it believes the preaching" (Freedom of the Christian)
The written Word (the Bible) "is not as fruitful and powerful as it is through a public preacher whom God has ordained to say and preach this.” (Sermon, 21 July 1532)
A Sample of Luther's Preaching
It would be spectacular and amazing, prompting all the world to open its ears and eyes, mouth and nose in uncomprehending wonderment, if some king’s son were to appear in a beggar’s home to nurse him in his illness, wash off his filth, and do everything else the beggar would have to do. Would this not be profound humility? Any spectator or any beneficiary of this honor would feel impelled to admit that he had seen or experienced something unusual and extraordinary, something magnificent.
But what is a king or an emperor compared with the Son of God? Furthermore, what is a beggar’s filth or stench compared with the filth of sin which is ours by nature, stinking a hundred times worse and looking infinitely more repulsive to God than any foul matter found in a hospital?
And yet the love of the Son of God for us is of such magnitude that the greater the filth and stench of our sins, the more He befriends us.
For how amazing it is that the Son of God becomes my servant, that He humbles Himself so, that He cumbers Himself with my misery and sin. . . . He says to me: “You are no longer a sinner, but I am. I am your substitute. You have not sinned, but I have. The entire world is in sin. However, you are not in sin; but I am. All your sins are to rest on Me and not on you.” No one can comprehend this. In yonder life our eyes will feast forever on this love of God. (Sermon on John 1:29)
And here's the lowdown on Luther and Preaching from David Lotz: HIGHLY RECOMMENDED