The general need of purification in the Christian congregations: V. 6. Your glorying is not good. Know ye not that a little leaven leaveneth the whole lump? V. 7. Purge out, therefore, the old leaven, that ye may be a new lump, as ye are unleavened. For even Christ, our Passover, is sacrificed for us; v. 8. therefore let us keep the feast, not with old leaven, neither with the leaven of malice and wickedness, but with the unleavened bread of sincerity and truth.
This case of the incestuous person was not the only matter which was wrong in the congregation at Corinth. It was true, in general, that their vaunt, that in which they made their boast, was not good, not of an acceptable quality. Among the members at Corinth there were many who led anything but model, pure lives, for which reason all vaunting and boasting on their part should have been omitted.
That their boasting was no credit to them, and that the corruption which was to be found in their midst should rather have caused the deepest humility among them, Paul proceeds to illustrate by a familiar comparison, by a proverbial saying: A little leaven leavens the entire mass, the whole kneading. A sin of this kind tainted the entire community. Just as the individual Christian cannot tolerate any sin, even the smallest, without corrupting his entire nature, just so an entire congregation will suffer the consequences if it permits so much as one of its members to continue in an open and flagrant offense.
"And herein this is the worst feature, that such corruption gains ground so powerfully and maintains its position so stubbornly that it cannot be eradicated again; just as the leaven, no matter how little is added to the dough, eats through it, so that everything is soon sour and no one can hinder it from becoming so, or make it sweet again" (Luther 12, 480).
For this reason Paul gives the advice: Clean out thoroughly the old leaven. He reminds his readers of the preparations for the ancient celebration of the Passover Festival. The removal of the leaven, Ex. 12, 18. 19, was done on the 13th or at the very latest on the morning of the 14th Nisan, and carried out with the most minute care. All the places in the house where bread was kept or where crumbs might have fallen were searched with lighted tapers, and all the dark corners scraped out carefully, lest any leaven remain to spoil the festival for the family. In just the same way the Corinthians must put from their midst the incestuous person and remove all open offenses. And even so the Christians of all times clean out the old leaven of sin by daily contrition and repentance in themselves and insist upon the application of the power to bind in case of notorious transgressions in church-members.
And the object of such purging, according to God's will, shall be: That you may be a new mass, just as you are unleavened. If a Christian uses care to keep down his own old Adam, and does all in his power to maintain the purity of the Christian congregation, then the will of God is realized in the gradual production of a hallowed mass, from which all evil ferment is removed, which is governed by the Spirit of God only. And the ability to accomplish so much is based upon God's gift of grace, the fact that all Christians are looked upon as unleavened, clean, and pure for the sake of Christ's atonement, John 15, 3.
"The apostle commands the old leaven to be swept out, and gives this reason: For you are a new mass and unleavened. To be a new or sweet mass he calls having the faith which clings to Christ and believes that it has forgiveness of sins through Him; as he shortly afterwards will say of Christ, our Passover, sacrificed for us, etc. Through the same faith we are cleansed of the old leaven, that is, from sins and an evil conscience, and have now begun to be new men. . . . Behold, that is one thing which this text teaches us, that also in the saints there yet remains weakness and much that is unclean and sinful, which is to be cleaned out, and yet is not imputed to them, since they are in Christ and purge out such leaven" (Luther 12, 483,485).
That the Christians are considered clean and pure before God through the merits of Christ, and should therefore endeavor to maintain this purity and keep their garments unspotted, is all based upon one fact: For our Passover also, Christ, is sacrificed for us. To people familiar with the customs of the Jewish festival the very suggestion must arouse their attention: The Passover lamb slain, and the leaven not yet cast out! It was intended to make them eager for all progress in Sanctification, and in every form, since all Christians are partakers of this wonderful gift. Christ is the true Passover Lamb, and all the festival lambs of the Old Testament were but types, pointing forward to the great fulfillment, Is. 53. Christ was sacrificed, slain, as a lamb that bore the sins of the world.
So great and terrible are the sins of the world that the great, serious, and terrible wrath of God because of sins, as Luther says, could not stop short of carrying out the decree of death in the case of the Substitute of all men. God spared not His own Son, but delivered Him up for us all. Thus Christ truly became our Passover; for His sake, for the blood which He shed, and which has been painted on the portals of our hearts, the angel of destruction passes by the believers, so that the plague of everlasting damnation cannot come nigh our dwelling.
All conditions being fulfilled in this manner: Let us, therefore, keep the feast, let us celebrate the festival meal and continue in the enjoyment of its blessings. And since, as Luther writes, we Christians have Easter always, since our Passover Lamb lasts forever, therefore the work of Sanctification which was begun in us in regeneration should continue throughout our lives; a consecrated life naturally follows from the intimate union between Christ and the believers.
This the apostle explains: Not in the old leaven, neither in the leaven of badness and meanness, but in the unleavened bread of sincerity and truth. The old leaven, everything that savors of the old sinful nature, has been purged out, it shall never again assume the rule in the hearts of the believers. And two specific manifestations of this old Adam are mentioned: the leaven of badness, of malice, of every trespass by which harm is inflicted upon our neighbor; and the leaven of meanness, of wickedness, whose object is to seduce men from the proper understanding of the Word and to work every manner of offense.
To this vicious disposition and the active exercise of it is opposed the keeping of the feast in the unleavened bread of purity and truth, a proper inward disposition that knows no guile, with which also accords a person's entire outward life, "that we both keep the pure doctrine of the Gospel and also with a holy life and example comport ourselves accordingly, and thus continually live properly, as on an eternal Easter festival, . . . wherein we, as new men in the faith of Christ, live and continue righteous, holy, and pure, in peace and joy of the Holy Ghost, as long as we are here on earth" (Luther 12, 488).