Although a rascal, a godless and unbelieving person, takes or gives the Sacrament, he takes or gives the true Sacrament, that is Christ's body and blood, just as truly as he who administers and receives it most worthily, so long as the Sacrament is celebrated as Christ has instituted and commanded it and the words of Christ are spoken. For the Sacrament is not based on the holiness of men but on the Word of God. And just as no saint on earth, yea, nor any angel in heaven, can make Christ's body and blood out of the bread and wine, just so no one can alter or change the essence of the Sacrament, even though it is misused. For the Word by which it was instituted and made a Sacrament does not become false because of a person's unbelief. For He does not say: If you believe or are worthy, you have My body and blood, but Take, eat and drink, this is My body and blood (Matt 26;26ff). (What Luther Says - pp. 795, 796, para 2473)
This passage was a reviving tonic to my heart in my trials concerning this Sacrament; and if we had no more passages than this one, we could nonetheless sufficiently confirm all consciences with it and forcefully enough refute all adversaries. ...Plainly and clearly St. Paul states: The very bread which we break is the communion of the body of Christ. do you hear, my dear brother? The broken bread, or the bread distributed in pieces, is the communion of the body of Christ. It is, it is, it is, says he, the communion of the body of Christ. but what is the communion of the body of Christ? It can consist in nothing else than this, that they who individually take a piece of the broken bread receive in it the body of Christ. (What Luther Says - p. 797 - para 2476)
While pointing at the bread, it is entirely correct to say: This is Christ's body, and whoever sees this bread sees Christ's body. Just so John said, as we heard, that he saw the Holy Spirit when he saw the dove. So we also rightly say: Whoever attacks this bread attacks Christ's body, whoever eats this bread eats Christ's body, and woever presses this bread with teeth or tongue presses the body of Christ with teeth or tongue. And yet it remains true in every respect that no one sees, grasps, eats or crushes Christ's body as other, visible flesh is seen and crushed. For what we do to the bread is correctly and well attributed to the body of Christ because of their sacramental union. (What Luther Says - p. 796 - para 2474)
The heart of man is a slippery thing: when matters go well, it falls into presumption; but when matters go badly, it falls into despair. This is why ours must be a mixed lot. God must throw one care after another into our prosperity, must salt it for us, and must dampen our high spirits with apprehension so that we stay with the First Commandment...Our troubles must also be tempered with some consolation so that we cling to God's promises and do not tempt God, who would be our God. In this way a man stays on the right road so that he does not despair in trouble but always stays standing and praises God, whether he fares well or ill, whether he wins or loses.
(What Luther Says - #682)
The life of a holy person consists more in taking from God than in giving, more in desiring than in having, more in becoming pious than in being pious; as St. Augustine says: Faith acquires what the Law requires. For this reason asking and seeking constitute the real mode of life of the inner man.
What Luther Says - para # 697, p. 234