Aliam parabolam locutus est eis : Similis est regnum caelorum fermento, quod acceptum mulier abscondit in farinae satis tribus, donec fermentatum est totum.
Another parable he spoke to them: The kingdom of heaven is like to leaven, which a woman took and hid in three measures of meal, until the whole was leavened.
During the great fire of 1906, so the story goes, Mrs Boudin ran into the family bakery to rescue a bit of the sourdough that was rising at that time, so that the strain of yeast in the 65 year old bakery could be continued. That strain is now 149 years old and still an SF favourite. It only take a little leaven.
Reaching the end of Christendom is scary for some folks. These folks define Christendom as a Majority World View and that majority is certainly passed away in the US, by falling off on the left and on the right. It died in Europe a painless death of under-use. Although it is thriving in many places, it is often woven in with leaders who would just as soon sell out for more power and mammon. Speaking ill of Putin got an Orthodox Parish in New York City slapped by the OCA. Catholics who are on the Trump train think the rest of us are fake Catholics. Christendom is dead, if by Christendom you mean the power to enforce our morality on folks who are not Christians by using the Gov't. Gov'ts don't care about us if we don't vote for them or else keep them in power.
Truth is, they never did.
Yet St Paul tells us to "honor the king" and "obey the laws" as long as they don't contravene the Law of God. And in that respect he's right - because he says the reason to do this is to get people to speak well of you and want to look into the Gospel. Jesus says, "Let your light shine before all that they may see your good deeds and praise God." St Paul takes the Roman Marriage and twists it into a loving relationship of equals. He wants to use it to convert the world. He turns slavery into Christian witness. He wants slave owners to do more than just treat their slaves as equals in Christ. He makes "law abiding" a way to preach. Jesus tells his disciples to be wise as serpents and to make friends of unrighteous mammon. Be in the world, but not of it. Two millennia later, the Christians of the CCCP were praying for the Soviets in the exact same words they used to pray for the Czar, asking that the Gov't would keep order so that the Church could live the Gospel.
Subversion, my friends. That's what this is about: subversion.
The Gospel is leaven, designed to change the world from the inside, or, as the Dominicans say, Grace builds on nature. God takes bread and makes it into His Body. God takes a sinner and makes her into a saint. God take humanity and makes it into himself. None of these by committing violence to the folks involved, but rather by leavening their loaf, by making them, from the inside, into what they are supposed to be. This is why there can be no Benedict Option. To abandon the world would be to rob the world of leaven.
Still this is not the way to victory. The death of Christendom only means a chance for us to die more often. "Actually I am a Christian,” Tolkien wrote, “and indeed a Roman Catholic, so that I do not expect ‘history’ to be anything but a ‘long defeat’— though it contains (and in legend may contain more clearly and movingly) some samples or glimpses of final victory.” (Letters 255).
The Apostles and all the Church Fathers tell us that no matter how hard we work to build God's kingdom here, the end will be the Kingdom of Antichrist and darkness.
But understand this, that in the last days there will come times of stress. For men will be lovers of self, lovers of money, proud, arrogant, abusive, disobedient to their parents, ungrateful, unholy, inhuman, implacable, slanderers, profligates, fierce, haters of good, treacherous, reckless, swollen with conceit, lovers of pleasure rather than lovers of God, holding the form of religion but denying the power of it. 2 Timothy 3:1-5a
It's not going to be pretty, either: Indeed all who desire to live a godly life in Christ Jesus will be persecuted, while evil men and impostors will go on from bad to worse, deceivers and deceived. And that "holding the form of religion" bit means that these folks will be (or at least claim to be) Christians. We have these today: folks who say the teachings of the church are impossible to keep, or who insist that a group or class of person can't keep the teachings of the Church so the teachings must change. In this they deny the power: of God to work, of the redemption of Christ to save, and of the human person to cooperate with grace.
The Council of Trent foresaw this:
If any one saith, that the commandments of God are, even for one that is justified and constituted in grace, impossible to keep; let him be Anathema. Canon XVIII
So we're right on target.
The Prophet Jeremiah's underwear is an amusing story. It's how these people will end up. But for the time, we have to even subvert the downward motion: for God intends it for our salvation. Being the leaven in the world, means being the sourdough of God. All we need is one pinch saved from the fire. Only a remnant will save the whole world.