Let's start with the basics:
The record-breaking Downton Abbey spans a deliciously long stretch of time. The show includes the wreck of the Titanic, in which the Crawley family loses its heir, the lead-up to World War I, the War itself, its aftermath, and now, in Season 3 (or "soon in Season 3," depending on where in the world you live and/or how good you are at locating British Broadcasting Corporation web feeds) the advent of the roaring 20's.
The show's writer and primary creative force, Julian Fellowes, is a practicing Catholic.
The show is set in an old abbey. The family who own Downton, especially the older generations who have the most to lose by losing the house, are obsessed not only with the house itself, but also with its history.
Also they employ a vicar.
So how is it that God is a peripheral presence at best?
To be fair, there have been a few mentions of God. During Season One there was a perfunctory scene set in a church, but it was basically about architecture. At the beginning of Season Two, the evil footman Thomas asked God's forgiveness for sticking his hand out of the trenches to be properly shot so he could return home with a medical discharge.
To be fairer still, Season Two included two moments of devout prayer: Lady Mary praying at her bedside when her beloved Matthew goes missing at the front, and two servants interceding for Matthew and another missing footman during the same period.
By some measures, this would be a watershed on a hit show—two scenes in which people sincerely pray! But in Downton, these events were so late in coming that they did more to point out a missed opportunity than to fill it.
There are a lot of characters in this show. The central "upstairs" cast includes a large family, various cousins and friends, and the local doctor. The central "downstairs" cast includes a similar host, from the cook's assistant to the chauffer.
During all these years of heartbreak, illness, transition, and death, the doctor was a regular fixture. But the vicar did not appear until halfway through Season 2. He had one set of lines, and if you went to pour your tea at the wrong moment, you probably missed him. During his brief appearance, we learned that the vicar lives on the family's land, and is beholden to Lord Grantham for both his livelihood and the flowers on his altar. Yet up to season 3 he seems to play less of a role in the household than the servants' new Ouija board.
Of course, any writer must choose which parts of his characters' lives to show and which to omit. We don't see Crawleys meeting with accountants, getting haircuts, or buying shoes—presumably because such events aren't very interesting (though I would be interested to see Maggie Smith's supremely witty Dowager Countess doing any of the three). Watching people go to church may not be much of a thrill either.
But what about the time- and genre-tested possibilities of a wily local vicar? In the poor man's one speaking scene (with Maggie Smith), he barely got a word in edgewise. How much deeper and more fun the show might be with a vicar—or some person of visible faith—who could match the Countess' wit and gravitas.
When he was appointed vice president of the Catholic Association of Performing Arts last year, Fellowes hinted that faith would enter Downton's central storyline in the near future.
Last year he also revealed that Downton Abbey's history is, in his conceit, similar to that of Highclere Castle, the house in which the show is filmed. This would mean that Downton was a convent or monastery before King Henry VIII appropriated it from the Catholic Church and either sold it or gave it to the Crawleys during the Reformation—or else the king let it pass to another family into which the Crawleys later married.