"If the article of justification is lost, all Christian doctrine is lost at the same time...for there is no middle ground between these two righteousnesses; the active one of the Law and the passive one which comes from Christ. Therefore the man who strays from Christian righteousness must relapse into the active one, that is, since he has lost Christ, he must put his confidence in his own works.
(What Luther Says, p. 702, para 2194).
To pray aright is a very difficult task and the art supreme. It is not so because of the words of the mouth. But for the heart to be able by itself to conclude with certainty and assurance that it may step before God with complete confidence and say; "Our Father" - that is a task.
(What Luther says - para 3477 - pp. 1088)
When you call upon Jesus Christ and say: O my dear Lord God, my Creator and Father, Jesus Christ, Thou one eternal God, you need not worry that the Father and the Holy Spirit will be angry on this account. They know that no matter which Person you call upon, you call upon all three Persons and upon the One God at the same time. For you cannot call upon one Person without calling upon the others, because the one, undivided divine Essence exists in all and in each Person. Conversely, you cannot deny any Person in particular without denying all three and the One God in His entirety, as I John 2:23 says: "Whosoever denieth the Son, the same hath not the Father."
(What Luther Says - para 3454, pp. 1082)
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)