Mark 9:50

Salt is good; but if the salt have lost his saltness, wherewith will ye season it? Have salt in yourselves, and have peace one with another.

Christ here mentions some other members that are very apt to offend, to commit sin, to lead others into sin. The law of sin is always active in our members. Here it is necessary that a person keep these members in subjection. For the Lord speaks figuratively and does not want to be understood, as Luther says, that He here advocates physical mutilation or dismemberment, since that would obviously not take the sin and the desire to sin out of the heart. It is the heart which must be controlled by the spirit of love toward Christ and our neighbor, in order that the hand, the foot, the eye do not perform that which sin desires them to do. Whosoever places his members into the service of sin, of uncleanness, and unrighteousness here in this life, will hereafter pay the penalty for such transgression in all eternity. But whosoever, with the help of the Holy Ghost, brings his members into subjection, trains them, holds his desires in check, does not permit sin to reign in his body, he will retain faith and a good conscience, he will keep body and soul unto life eternal. Note: This passage makes such a deep impression on account of the earnestness of the Savior and because of His solemn reference to the fire of hell, and to the worm that will not die, and to the fire that will not be quenched. The fires of the Valley of Hinnom, near Jerusalem, where all the refuse of the city was burned, were commonly taken as a type of the fires of hell. As these fires burned without ceasing, day and night, so the fires of hell will offer no respite. And as the worms were continually feeding on the remains of carcasses and refuse that was dumped out into that valley, so some of the torments of hell will be like the ceaseless gnawing of worms. To try to crack jokes at the expense of the doctrine of hell, or to deny this doctrine outright, for the flimsiest reasons, is decidedly blasphemous in view of such passages as the present and Luke 16:28.

This sacrifice, this continual working and bringing into subjection one's own members for the sake of Christ, is demanded by Christ in the interest of His purpose to make every Christian and the entire Christian Church a salt in this world. As every sacrifice of the Old Testament had to be salted, Leviticus 2:13, so every disciple, every believer, must be salted with fire. Jesus does not refer, in this instance, to the fire of hell, but to the purifying fire of His rule and leading. It is the discipline of the Word and the Spirit of God which gradually cleanses the believers of sin, and kills the works and desires of the flesh, and the fire of tribulation, which renders sin and its results unpleasant, 1 Peter 1:4. This fire incidentally performs the work of a salt, it prevents moral rotting and a relapse into the service of sin. And the Christians that have been sanctified by the Word and the Spirit of God and whose sanctification is progressing continually should have this salt with them always, in doctrine and admonition. They shall freely, as occasion offers, rebuke the false works of the world, instead of permitting the world to lead them into sin. But among themselves, one with another, they should maintain peace and not boastingly seek self-glorification. The fact that the Gospel is a salt is brought out strongly by Luther in admonishing the Christians to be a true salt. "Where the salt loses its saltiness, and the Gospel is spoiled with doctrines of men, there the old Adam no longer can be spiced, there the worms will grow. But salt is sharp; therefore it is necessary to have patience and peace in the salt."

Summary. After the miracle of the transfiguration, Jesus heals a deaf-mute boy, gives His disciples information concerning their inability to cast this demon out, announces His Passion for the second time, and gives them a long discourse on service, humility, and on giving offense.