Your glorying is not good. He condemns their glorying, not simply because they extolled themselves beyond what is lawful for man, but because they delighted themselves in their faults. He had previously stripped mankind of all glory; for he had shown that, as they have nothing of their own, whatever excellence they may have, they owe the entire praise of it to God alone. (1-Corinthians 4:7.) What he treats of here, however, is not that, God is defrauded of his right, when mortals arrogate to themselves the praise of their excellences, but that the Corinthians are guilty of arrant folly in extolling themselves without any just ground. For they proudly gloried as if everything had been in a golden style among them, while in the meantime there was so much among them that was wicked and disgraceful. Know ye not That they might not think that it was a matter of little or no importance that they gave encouragement to so great an evil, he shows the destructive tendency of indulgence and dissimulation in such a case. He makes use of a proverbial saying, by which he intimates that a whole multitude is infected by the contagion of a single individual. For this proverb has in this passage [1] the same meaning as in those expressions of Juvenal: "A whole herd of swine falls down in the fields through disease in one of their number, and one discolored grape infects another." [2] I have said in this passage, because Paul, as we shall see, makes use of it elsewhere (Galatians 5:9) in another sense.

Footnotes

1 - "Ha en ce passage un mesme sens comme ce qu'on dit communeement, Qu'ilne faut qu'vne brebis rongneuse pour gaster tout le troupeau;" -- "Has in this passage the same meaning as what is commonly said: -- There needs but one diseased sheep to infect a whole flock."

2 - -- grex totus in agris Unius scabie cadit, et porrigine porci: Uvaque conspecta livorem ducit ab uva Juv. II. 79-81.

Your glorying - Your boasting; or confidence in your present condition, as if you were eminent in purity and piety.
Is not good - Is not well, proper, right. Boasting is never good; but it is especially wrong when, as here, there is an existing evil that is likely to corrupt the whole church. When people are disposed to boast, they should at once make the inquiry whether there is not some sin indulged in, on account of which they should be humbled and subdued. If all individual Christians, and all Christian churches, and all people of every rank and condition, would look at things as they are, they would never find occasion for boasting. It is only when we are blind to the realities of the ease, and overlook our faults, that we are disposed to boast. The reason why this was improper in Corinth, Paul states - that any sin would tend to corrupt the whole church, and that therefore they ought not to boast until that was removed.
A little leaven - A small quantity of leaven or yeast will pervade the entire mass of flour, or dough, and diffuse itself through it all. This is evidently a proverbial saying. It occurs also in Galatians 5:9. Compare the note at Matthew 13:33. A similar figure occurs also in the Greek classic writers - By leaven the Hebrews metaphorically understood whatever had the power of corrupting, whether doctrine, or example, or anything else. See the note at Matthew 16:6. The sense here is plain. A single sin indulged in, or allowed in the church, would act like leaven - it would pervade and corrupt the whole church, unless it was removed. On this ground, and for this reason, discipline should be administered, and the corrupt member should be removed.

Your glorying is not good - You are triumphing in your superior knowledge, and busily employed in setting up and supporting your respective teachers, while the Church is left under the most scandalous corruptions - corruptions which threaten its very existence if not purged away.
Know ye not - With all your boasted wisdom, do you not know and acknowledge the truth of a common maxim, a little leaven leaveneth the whole lump? If this leaven - the incestuous person, be permitted to remain among you; if his conduct be not exposed by the most formidable censure; the flood-gates of impurity will be opened on the Church, and the whole state of Christianity ruined in Corinth.

(7) Your glorying (d) [is] not good. Know ye not that a little leaven leaveneth the whole lump?
(7) Another goal of excommunication is that others are not infected, and therefore it must of necessity be retained in the Church, so that one is not infected by the other.
(d) Is nothing and not grounded upon good reason, as though you were excellent, and yet there is such wickedness found among you.

Your glorying is not good,.... Their glorying in their outward flourishing condition, in their riches and wealth, and in their ministers, in their wisdom and parts when under such an humbling dispensation; and especially if their glorying was in the sin itself, and their connivance at it, it was far from being good, it was very criminal, as the consequence of it was dangerous:
know ye not that a little leaven leaveneth the whole lump? This, in nature, is what everybody knows; and the proverb, which is much used by the Jews (f), was common in the mouths of all, and the meaning of it easy to be understood: thus, whether applied to the leaven of false doctrine, nothing is more manifest, than when this is let alone, and a stop is not put to it, it increases to more ungodliness; or to vice and immorality, as here; which if not taken notice of by a church, is not faithfully reproved and severely censured, as the case requires, will endanger the whole community; it may spread by example, and, under the connivance of the church, to the corrupting of good manners, and infecting of many.
(f) Neve Shalom apud Caphtor, fol. 41. 1.

Your glorying in your own attainments and those of your favorite teachers (1-Corinthians 3:21; 1-Corinthians 4:19; 1-Corinthians 5:2), while all the while ye connive at such a scandal, is quite unseemly.
a little leaven leaveth . . . whole lump-- (Galatians 5:9), namely, with present complicity in the guilt, and the danger of future contagion (1-Corinthians 15:33; 2-Timothy 2:17).

Your glorying is not good. Boasting, in such a state of affairs, was unseemly.
A little leaven, etc. As a little leaven leavens the whole mass of dough, so one sinner suffered to go on in impurity sends a corrupting influence through the whole church.
Purge out therefore the old leaven. Let the leaven of impurity be removed, by putting out the fornicator, that the church may be pure from the impure leaven, or influence. So, too, each one must cleanse his own heart.
For even Christ our passover, etc. At the passover, Jews were required to put all leaven from their houses (Exodus 12:15). As we have a Paschal Lamb, slain for us, the church should cleanse out the leaven of sin.
Let us keep the feast. Let us keep feast, or festival. There is no article in the Greek. The reference is not to the Lord's Supper, or to Easter, as some have supposed, so much as to a constant duty. We always have a Paschal Lamb; hence it is always our duty to keep festival by casting out all leaven; either the old leaven of heathen vice, or of malice and wickedness, or any sin.

Your glorying - Either in your gifts or prosperity, at such a time as this, is not good. Know ye not that a little leaven - One sin, or one sinner. Leaveneth the whole lump - Diffuses guilt and infection through the whole congregation.