Our Lord Jesus Christ says: “You are already made clean by the Word which I have spoken to you.” Dr. Martin Luther comments this vers – and here´s some of that audible in German – readings of John 15,3 in “Luthers Evangelien-Auslegung 4.Teil.” ed. Eduard Ellwein. Vandenhoek: Göttingen, 1954. Pg.444-445: Teil 1 und Teil 2.

This is a peculiar cleansing. What Christ says here seems to contradict His previous words, which deal with suffering and the cross. It sounds like a thought just thrown in. Yet with these words Christ offers us a fine preservative or remedy against the poison called presumption or overestimation of one’s own holiness, lest anyone think that through suffering he obtains forgiveness of sins and becomes a branch in the sight of God without Christ. For this is the natural sequence: After a person has performed many good works or has suffered much and is aware of the fruit he bears—by an extraordinary achievement in preaching or in some other way—then that sweet poison always stealthily injects itself to make him think: “Well, after all, I have accomplished something which God will approve of and in view of which He will show me mercy.” Thus nature always sprouts such secondary or wild branches as want to grow along with the true branches, deprive these of their sap and strength, and stunt their growth. Therefore the Vinedresser must be alert here at all times and restrain such a false notion and such presumption by a constant application of the Word.
For this reason Christ now says: “You are not clean by virtue of your deeds, your suffering, and your fruit; for you would not have borne this fruit if you had not previously been pruned and become good and true branches. The cleansing process must be carried out through the Word, which must be present at all times and must cleanse you both before and after. But in order that it may have power in you, be surely apprehended and firmly retained by you, the Father sends you many kinds of suffering, peril, anxiety, distress, and affliction, to humble you and to teach you that the cleanness does not proceed from you and is not of your own doing. Therefore your suffering is not the cleanness itself, and you are not declared clean in the sight of God because of it. But it does serve to drive man to grasp and hold the Word with a better and firmer grip, in order that in this way faith may become active. The Word is itself the purification of the heart if the heart adheres to it and remains faithful to it.
Christ states clearly: “You are already made clean by the Word which I have spoken to you” (John 15:3). This is nothing else than Christ’s entire sermon: He was sent into the world by the Father to redeem us from our sin by His suffering and death, and to reconcile us to the Father, that all who believe in Him might not be damned and lost but have remission of sin and eternal life for His sake. This Word makes man clean when the heart takes hold of it in faith; that is, it brings forgiveness of sin and makes man acceptable to God. On account of this faith, by which alone the Word is received and apprehended, we who adhere to it are accounted completely pure and holy before God, even though we—because of our nature and our life—are not clean enough but during our sojourn on earth are always infected with sin, weakness, and shortcomings, which must still be purged.
Thus Christ teaches the real core of Christian doctrine with these words; He shows how and by what means man is purified and justified before God. These words teach that the cleansing from sin which is valid before God should not be attributed to our deeds or suffering, even though these are performed by and happen to Christians and are now termed true, good, and pure fruits. For here Christ is referring to His beloved apostles, who were now believers, or Christians. He says: “You are already made clean” (John 15:3), yet not by reason of their good fruits but “by the Word which I have spoken to you.” How does this take place? How can they be unclean and clean at the same time? If they are clean, why does Christ say that they must constantly be made clean? Or why do they pray in the Lord’s Prayer “Forgive us our trespasses,” and “Thy will be done,” thereby confessing, of course, that they are still sinful and unclean? For he who asks for forgiveness of sin and deplores that God’s will has not been done cannot be called clean. On the other hand, if they are unclean and must still be cleaned, how, then, can Christ call them clean? How do you reconcile this?
Answer: As I have said, man is first declared clean by God’s Word for Christ’s sake, in whom he believes. For by such faith in the Word he is grafted into the Vine that is Christ and is clothed in His purity, which is imputed to him as his own and is as perfect and complete in him as it is in Christ. All this happens through the Word, if it is received and accepted in faith. There I hear God’s will and promise that He will forgive my sins for Christ’s sake and will adjudge and regard me as clean. And when I lay hold of the Word by faith, it creates in me—through the Holy Spirit, who works through it—a new heart and new thoughts, which adhere to it firmly and do not doubt but live and die by it. Because I cleave to it, for this reason whatever impurities and sins still cling to me are not imputed to me; but this weak, imperfect, and inchoate purity is reckoned as wholly perfect purity. God makes the sign of the cross over it and acknowledges it, and He closes an eye to the uncleanness that still remains in me. And where such cleanness comes into being through the Word in faith, God proceeds to improve and perfect it by cross and suffering, so that faith is increased and the remaining uncleanness and sin are daily diminished and purged until death. That is what Christ means when He speaks, as He does above, of constantly pruning and cleaning the branches on the vine that are now clean by the Word.
Behold, thus Christ shows clearly that the cleanness of Christians does not come from the fruit they bear but that, conversely, their fruit and works spring from the cleanness which they already have from the Word, by which the heart is cleansed. That is what St. Peter states in Acts 15:9. Though the fruit grows from this cleanness, it itself is not the cleanness; but it is accounted clean and good and pleasing to God for the sake of faith. This is the Christian doctrine of true purity, which is so incomprehensible to any non-Christian, papist, or schismatic spirit, who is unable to reconcile the two facts that a Christian is clean and unclean at the same time. They are ignorant of the power of Christ and of His Word, of how we are declared wholly clean for His sake through the Word, as clean as He Himself is, although in ourselves we still are, and always will be, impure because of our sinful nature. The devil will never find a flaw in the Word or prove it false; nor will he succeed in making Christ unclean. And since the Word is right and true, and since Christ remains pure, we will also be and remain pure and holy in Him. And no one will ever make us unclean or sinners. At the same time such cleansing will also bear good fruit in us, as Christ has stated (v. 2).

Dr Martin Luther in “Luther Works” Vol.24

Zum Abschluß das dazu passende Glaubenslied des Johann Agricola (1530):

Ich ruf zu dir, Herr Jesu Christ, ich bitt, erhör mein Klagen; verleih mir Gnad zu dieser Frist, lass mich doch nicht verzagen. Den rechten Glauben, Herr, ich mein, den wollest du mir geben, dir zu leben, meim Nächsten nütz zu sein, dein Wort zu halten eben.

Ich bitt noch mehr, o Herre Gott – du kannst es mir wohl geben –, dass ich nicht wieder werd zu Spott; die Hoffnung gib daneben; voraus, wenn ich muss hier davon, dass ich dir mög vertrauen und nicht bauen auf all mein eigen Tun, sonst wird’s mich ewig reuen.

Verleih, dass ich aus Herzensgrund den Feinden mög vergeben; verzeih mir auch zu dieser Stund, schaff mir ein neues Leben; dein Wort mein Speis lass allweg sein, damit mein Seel zu nähren, mich zu wehren, wenn Unglück schlägt herein, das mich bald möcht verkehren.

Lass mich kein Lust noch Furcht von dir in dieser Welt abwenden; beständig sein ans End gib mir, du hast’s allein in Händen; und wem du’s gibst, der hat’s umsonst, es mag niemand erwerben noch ererben durch Werke deine Gunst, die uns errett’ vom Sterben.

Ich lieg im Streit und widerstreb, hilf, o Herr Christ, dem Schwachen; an deiner Gnad allein ich kleb, du kannst mich stärker machen. Kommt nun Anfechtung her, so wehr, dass sie mich nicht umstoße; du kannst machen, dass mir’s nicht bringt Gefähr. Ich weiß, du wirst’s nicht lassen.