Luther had the following to say “On Maintaining Friendship and Love,” Commentary on the Gospel of St. John, volume 24, pages 244-246.
It is inevitable that one member occasionally jostles the other, just as a foot or a toe of our body bumps the others, or as a person injures himself. Such bumps and trials do not fail to come, especially because we are sojourning here in the realm of the devil, who tempts us uninterruptedly, and also because the flesh is still weak and full of flaws. This explains why even dear and faithful friends fall out or become irritable with one another.
At times the devil injects poison and suspicion into a heart because of a single word or glance and thereby stirs up mutual animosity. He is a master in this art and devotes himself to it most diligently. He employs his craftiness before one is really aware of it. As we read in Acts 15:2, this is what he did in the case of St. Paul and Barnabas, who had a sharp dissension and parted company.
Or take the two men Jerome and Rufinus, who had been the best of friends and like brothers. They quarreled over a preface and were unable to reestablish their former friendship. The same thing would have happened between St. Augustine and Jerome if Augustine had not been so shrewd. Trifles can lead to such quarreling and enmity that great harm results to many. The blood soon begins to boil; then the devil shoots his venomous darts into the heart by means of evil tongues, and finally no one says or thinks anything good about the other person. The devil keeps on fanning the flames and is eager to set people against one another, to spread misery, and to incite them to murder.
According to a story — it may have been invented, but it serves very well to illustrate the devil’s cunning — a certain husband and wife loved each other so dearly that the devil was unable to alienate them from each other as he wished. Finally he bribed an old witch with the promise of a pair of red shoes to sow discord between the two. She accepted the offer.
First she went to the husband and convinced him that his wife was a whore, felt an attraction for another man, and had designs on his life. In proof of this, she said, he would find under his wife’s pillow a sharp razor with which she intended to cut his throat at night. The husband swallows the poison and begins to grow suspicious. Meanwhile the old whore also approaches the wife with the very same story. She tells the wife that her husband is chasing after other women and is planning to kill her stealthily. She advises her to anticipate her husband and take a razor to bed with her. Henceforth the two did not have a friendly word or show each other a single token of love the whole day long. The wife took the razor to bed with her, the very razor for which her husband was lying in wait. And when he discovered it, he seized it and cut her throat.
It is also related — and it sounds credible — that the devil then put the shoes on a pole to hand them to the old hag and said: “I do not want to come near, for you are far more evil than I.”
Therefore it behooves us Christians to be on our guard against the devil’s craft and cunning, to exercise prudence, and to beware of letting such poison develop in our hearts. We must repel any suspicion and antipathy that may be stirred up in us and remind ourselves not to let love depart and die out for this reason but to hold to it with a strong hand. And if aversion and discord have arisen anywhere, we must restore and improve the love and friendship.
It does not require such great skill to begin to love; but, as Christ says here, remaining in love takes real skill and virtue. In matrimony many people are initially filled with such ardent affection and passion that they would fairly eat each other; later they become bitter foes. The same thing happens among Christian brethren. A trivial cause may dispel love and separate those who should really be bound with the firmest ties; it turns them into the worst and bitterest enemies. That is what happened in Christendom after the days of the apostles, when the devil raised up his schismatic spirits and heretics, so that bishops and pastors became inflamed with hatred against one another and then also divided the people into many kinds of sects and schisms from which Christendom suffered terrible harm.
That is the devil’s joy and delight. He strives for nothing else than to destroy love among Christians and to create utter hatred and envy. For he knows very well that Christendom is built and preserved by love. In Col. 3:14 Paul speaks of love as “binding everything together in perfect harmony.” And in 1 Cor. 13:13 he calls love the greatest virtue, which accomplishes and achieves most in the Christian realm. For in the absence of love doctrine cannot remain pure; nor can hearts be held together in unity.
Therefore Christ admonishes us so solemnly and earnestly to hold firmly to love above all else after we have come to faith in Him and are now His branches. He places both Himself and His Father before our eyes as the noblest and most perfect examples: “As My Father has loved Me, so have I loved you; abide in My love.” He wants to say: “My Father loves Me so much that He transmits all His power and might to Me. To be sure, He lets Me suffer now; but He takes to heart all that I do and suffer as though this were happening to Him, and He will raise Me from the dead, make Me Lord over all things, and completely glorify His divine majesty in Me. So do I love you. I shall not leave you in your sins and in death, but I will stake life and limb to rescue you. And I shall communicate to you My purity, holiness, death, resurrection, and all that I can do.”