1 Corinthians 5:6-13
6 Your boasting is not good. Do you not know that a little leaven leavens the whole lump? 7Cleanse out the old leaven that you may be a new lump, as you really are unleavened. For Christ, our Passover lamb, has been sacrificed. 8Let us therefore celebrate the festival, not with the old leaven, the leaven of malice and evil, but with the unleavened bread of sincerity and truth.
9I wrote to you in my letter not to associate with sexually immoral people— 10 not at all meaning the sexually immoral of this world, or the greedy and swindlers, or idolaters, since then you would need to go out of the world. 11But now I am writing to you not to associate with anyone who bears the name of brother if he is guilty of sexual immorality or greed, or is an idolater, reviler, drunkard, or swindler—not even to eat with such a one. 12For what have I to do with judging outsiders? Is it not those inside the church whom you are to judge? 13God judges those outside. "Purge the evil person from among you."
Catholics act as though it matters not how immoral their church becomes as long is their church is pure in doctrine. So long as their church condemns immorality on paper, the fact that it tolerates or even facilitates immorality in practice can never cast doubt on the claims of Rome.
Let’s compare this attitude with Paul’s ecclesiology. Here is what a Catholic scholar has to say about 1 Cor 5:1-13:
“The motivation for the remedy that Paul is applying to this situation in the Corinthian community is double: (a) eschatological: in view of judgment on the Day of the Lord (5:5); and (b) Christological: expressed in another metaphor, this time drawn from the baking of bread and the annual celebration of Passover. In the making of bread, a bit of leaven ferments the whole batch of dough. Immorality and other evil conduct have contaminated the community like ‘old leaven,’ because they have produced their evil effects in its corporate life. As Jews used to clear out their houses on the eve of Passover all leavened products, so Corinthian Christians must now clear out of their midst the ‘old leaven,’ that they may celebrate the Christian Passover, and also that they may become ‘unleavened,’” J. Fitzmyer, First Corinthians (Yale (2008), 230.
“The passage deals with what later came to be called ‘excommunication,’ for Paul recommends not only that ‘the one who has done this should be removed from your midst’ (v2c; cf. v13b), but that Corinthian Christians should not associate with immoral fellow Christians (vv9-11)…The roots of such exclusion are found in the OT…The reason for the exclusion was the corporate responsibility of Israel, if the wrongdoer were not cut off, as in the prayer of Moses and Aaron in Num 16:22, ‘O God, God of the spirits of all flesh, (if) one man’s sins, will you be enraged against the whole congregation?’” ibid. 231.
“[v5] In the long run, Paul is not so much concerned about the sin of the individual as he is about the smugness of community members in tolerating such a wrongdoer among them, which jeopardizes their status in God’s sight and will not be in their interest on the Day of the Lord; hence his recommendation of the exclusion of all that is immoral,” ibid. 240.
“[vv6-7] Paul’s rhetorical question quotes a common popular proverb [‘A little leaven ferments the whole batch of dough’], as also in Gal 5:9. The proverb suggests that it takes only one small instance of improper sexual conduct to contaminate the whole community; cf. the proverb cited in 15:33, ‘Bad company corrupts good habits.’ Christians of Roman Corinth are to clear out from their midst that which has made it impossible for them to be celebrating the new Passover. One corrupt member in their midst is enough to make the whole community unworthy,’” ibid. 240.
“[v13] Paul concludes this discussion of sexual immorality with a modified quotation of Deut 17:7…Thus, Paul uses the OT to bolster up his judgment already expressed in vv2c,5a,11a above, but not so bluntly as here. The Christian community is obliged to preserve its sanctity by excluding the wrongdoer from its mist, which is ‘the main point of the passage,’” ibid. 244-45.
By contrast, not only has the Roman hierarchy make no concerted effort to eradicate immorality from the priesthood, it has made a concerted effort to conceal and thereby propagate and perpetuate such immorality.