Consider therefore, my dear children, what great advantage you have, if you willingly hear and learn the Word of God. Learn, first of all, that you are of God, having conquered the devil and hell, so that neither sin nor the judgment of God can terrify. You will also be enabled to endure calmly other annoyances which, though they be ever so trifling, make the world impatient and hopeless. It is true, the Christians must suffer much from the devil and the world, their bitter enemies. Their body and life, their possession and honor are often in great danger. How shall they endure all this with patience? In no other way than by clinging to the promises of God, so that they can exclaim: Let the world wag and do as it pleases, I am not of her, but of God, else would the world be my friend; but I prefer that she should hate and harass me on every side, to having her good will and then to be not of God. If the heart is thus minded, all tribulation and adversity will pass by as do the clouds in the sky or the birds in the air; we see them for a time and then no more. Our only comfort in this life must be the possession of the Word and its power, especially when the last hour comes, when death approaches. If we believe the Word with a childlike faith, death will be as a sleep to us. Yea, it will be as when one who journeys along in a dense mist is attacked and slain before he is aware of the presence of the murderer. The devil is indeed a murderer, who has determined upon our death; we know that well. But this his threat and sure attack shall not alarm us. We have the Word, to it we cling; that causes resignation, joy and courage in the presence of dire visitations, even of death. The confidence that through Christ we have in heaven a Father, kind and merciful, will give us strength and patience to endure with true fortitude all the trials of life to the end. This consolation we find in the Word, and nowhere else. (Luther’s House Postil, Sermon for Judica, Volume 1, p. 298-299)

… Christ says: “He that heareth not the words of God is not of God, but is the devil’s child.” The most deplorable circumstance in this connection is the infatuation, in which these defamers of God’s Word live, so that they do not perceive the error of their ways, but defend their conduct with bitter resolution. Thus did the Jews; they answered Christ: “Say we not well that Thou art a Samaritan, and hast a devil? A self-righteous devil, who thinks that he is always right, is the worst of all devils; and such an one was prompting the Jews. This is the first lesson taught in our Gospel, that they who will not hear the Word of God are not of Him, but of the devil. This, of course, does not mean that the devil created such persons with their body, mind and all they possess. No, God bestowed upon them these gifts, wherefore we must distinguish between the abilities of man and their use. The man who lies and cheats has a good tongue given to him by God, but the use which he makes of it is of the devil in whose service he abuses it against God. Thus also God may give to man beautiful and charming eyes, but their employment for lustfulness is of the devil. If the heart yearns after lewdness, falsehood and deceit, it is wicked and of the devil, in respect to its use, though it be good and of God as to its essence.

On the other hand, “to be of God” means to employ willingly and gladly the ears in hearing the Word of God, and to accept rebuke for that which is wrong. Thus we should also use the tongue to pray, to preach, to instruct and to give consolation. Ears and tongues thus engaged are of God and good; they accomplish the purpose for which they were given. The heart also, if it meditates upon that which is comely, upon what is beneficial for our fellow men, and does not give offense, is a creature of God as well as the ears and the tongue. It is of God, because it strives to follow the precepts of God, and loves to hear His Word, and shuns everything opposed to it. It may happen, alas! that we are overtaken unaware by our weakness; that we curse where we ought to pray, and give way to anger where we ought to manifest kindliness; but if we see our wrong and confess it, asking for mercy, we may then indeed have wavered, or even fallen, but we are not yet of the devil. If a man repents of his sins, and turns to God with the firm resolution to avoid that which is wrong, he will obtain mercy, and the devil is not his master. (Luther’s House Postil, Sermon for Judica, Volume 1, p. 296-297)