I came across some remarks by Luther about painting that are very good examples of the Biblical understanding that is somewhat unique to Lutheranism: whatever communicates God’s Word faithfully is truly considered to be the Word of God. The key is that it must be faithful to the authoritative revelation of the Word of God: the Scriptures. We Lutherans, unlike the Reformed, do not despise music or the visual arts as vehicles for God’s Word. As regular readers of this blog site know, I lament the impoverished state of the visual arts in Lutheranism. The thought that a bare, sterile interior of a church is somehow more "spiritual," than one that has beautiful decoration and paintings is a notion foreign to the Bible and to Lutheranism. CFW Walther once observed that the worship spaces of the Reformed look like little more than sparse lecture halls; whereas, Lutheran churches are clearly seen to be true temples dedicated to the worship of the Living God. Let’s here Luther on the value of painting. His quotes are in itals, source following:
God’s Word is presented so powerfully, lucidly, and clearly in preaching, singing, speaking, writing, and painting that they must concede it is the true Word of God. 
Therefore David put this blessing at the end, where a song should sound best. Who can completely express the greatness of this gift? For who can exhaust all the virtue and power of God’s Word? The Holy Scriptures, sermons, and all Christian books do nothing but praise God’s Word, as we also do daily in our reading, writing, preaching, singing, poetizing, and painting. This blessing abides and sustains us when the temporal blessings vanish and when through death we part from them and from one another. This blessing does not leave us or part from us; it goes through death with us, tears us out of it, and brings us to eternal life, where there is neither death nor fear of dying. But of this more later. 
Consider our own times, in which we are preaching of the grace of Christ against our own presumptuous works and holiness. How few there are to see this or to accept it earnestly! Where does the fault lie? It is being preached and taught so lucidly; it is being read, written, sung, painted, and disseminated in every way, so that wood and stone could understand it if these were endowed with but a modicum of reason.
Here again the interpreters are toiling and disagreeing. There was a similar command in chapter 8:11 above. This is customary procedure with the prophets: When the ungodly refuse to believe the bare Word, the prophets add an external sign. So Jeremiah, getting no results when he predicted the Babylonian captivity, wore a chain around his neck as an external sign (Jer. 27:2). So here the writing drawn on the tablet is a sign. Thus in our time the Word is read and taught by means of the tongue, the pen, songs, and paintings as a witness to the ungodly. 
There has been enough preaching, writing, printing, reading, singing, speaking, and painting. By this time they ought to realize that Christ is not a serpent, a vile worm, a dragon, or a demoniac, as His slanderers claim, but the Savior of all who believe in Him. Yet they wantonly refuse to believe it. Let them perish! But we know that He grants us salvation, that He is given to us by God as our King and Lord or Savior, and that God made Him a Wisdom for Jews and Gentiles which no reason can fathom. He is also our Resurrection, as He Himself declares: “I shall rise again, and all who accept Me and believe in Me will rise from the dead and ascend into heaven.” 
Thus Christ Himself says in Matt. 11:5: “The blind receive their sight, the lame walk, the dead are raised up.” They are confronted by this twofold and powerful testimony.48 “Therefore neither I nor My Father can be blamed for the fact that they do not, and do not want to, know Me; their wickedness is to blame. Similarly, we can also say of our adversaries that they cannot adduce ignorance of the Gospel’s doctrine as an excuse. For we have preached it to them, painted it for them, written and sung it to them; and they have heard it and read it, yes, they themselves have attacked it in their writings. 
I have myself seen and heard the iconoclasts read out of my German Bible. I know that they have it and read out of it, as one can easily determine from the words they use. Now there are a great many pictures in those books, both of God, the angels, men and animals, especially in the Revelation of John and in Moses and Joshua. So now we would kindly beg them to permit us to do what they themselves do. Pictures contained in these books we would paint on walls for the sake of remembrance and better understanding, since they do no more harm on walls than in books. It is to be sure better to paint pictures on walls of how God created the world, how Noah built the ark, and whatever other good stories there may be, than to paint shameless worldly things. Yes, would to God that I could persuade the rich and the mighty that they would permit the whole Bible to be painted on houses, on the inside and outside, so that all can see it. That would be a Christian work. 
A cemetery rightfully ought to be a fine quiet place, removed from all other localities, to which one can go and reverently meditate upon death, the Last Judgment, the resurrection, and say one’s prayers. Such a place should properly be a decent, hallowed place, to be entered with trepidation and reverence because doubtlessly some saints rest there. It might even be arranged to have religious pictures and portraits painted on the walls. 
I do not think it wrong to paint such stories along with the verses on the walls of rooms and chambers so that one might have God’s words and deeds constantly in view and thus encourage fear and faith toward God. And what harm would there be if someone were to illustrate the important stories of the entire Bible in their proper order for a small book which might become known as a layman’s Bible? Indeed, one cannot bring God’s words and deeds too often to the attention of the common man. Even if God’s word is sung and said, preached and proclaimed, written and read, illustrated and pictured, Satan and his cohorts are always strong and alert for hindering and suppressing God’s word. Hence our project and concern is not only useful, but necessary—in fact, very badly needed. I don’t care if the iconoclasts condemn and reject this. They do not need our advice and we don’t want theirs, so it is easy for us to part company. I have always condemned and criticized the misuse of [religious] pictures and the false confidence placed in them and all the rest. But whatever is no misuse of pictures I have always permitted and urged the use of for beneficial and edifying results. This is the way we teach our common people; those clever fellows shall be neither our pupils nor our masters. May Christ be with an who believe in him and love him. Amen. 
It is most surprising to me that anyone can claim that I reject the law or the Ten Commandments, since there is available, in more than one edition, my exposition of the Ten Commandments, which furthermore are daily preached and practiced in our churches. (I am not even mentioning the Confession and the Apology and our other books). Furthermore, the commandments are sung in two versions, as well as painted, printed, carved, and recited by the children morning, noon, and night.6 I know of no manner in which we do not use them, unless it be that we unfortunately do not practice and paint them with our deeds and our life as we should. I myself, as old and as learned as I am, recite the commandments daily word for word like a child. So ff anyone perchance gained some other impression from my writings and yet saw and perceived that I stressed the catechism so greatly, he might in all fairness have addressed me and said, “Dear Dr. Luther, how is it that you emphasize the Ten Commandments so much, though your teaching is that they are to be discarded?” That is what they should have done, and not worked secretly behind my back and waited for my death, after which they could make of me what they would. Ah well, let them be forgiven who cease doing this. 
Go the extended entry for the footnotes.