OUR intervention in Syria required me to be fully serious last Sunday, but now it’s time to return to this column’s ongoing series of implausible proposals, Easter Sunday edition. Which means I’ll be proposing — yes, I’m that predictable — that many of this newspaper’s secular liberal readers should head en masse to church.

But not by converting to my own religion, Roman Catholicism. Of course that’s what I really want, what the sinister albino monk at my shoulder keeps muttering about, what the mimeographed orders from Catholic central command expect me to eventually achieve. (All those “disagreements” I keep having with Pope Francis are just classic papist trickery.)

For now, though, let’s talk about a smaller leap of faith. A large share of well-educated liberal America is post-Protestant — former Methodists, ex-Lutherans, lapsed Presbyterians, the secularized kids of Congregationalists. Their ancestral churches, the theologically-liberal mainline denominations, are aging and emptying, with the oldest churchgoing population and one of the lowest retention rates of any Christian tradition in the United States.

As a conservative Catholic, I have theories about how this collapse reveals the weaknesses of liberalism in religion. But my theological-sociological vindication isn’t worth the cost of mainline Christianity’s decline. For the sake of their country, their culture and their very selves, liberal post-Protestants should find a mainline congregation and starting attending every week.