Note: No spoilers for the season finale, but we figured the rest of season 3 is fair game for discussion.

In the third season finale of Downton Abbey, which airs Sunday night on PBS, series creator Julian Fellowes puts the cap on perhaps the most uneven—but definitely the most spiritual—season yet of his colossal hit. He's more than made good on his (somewhat unofficial) declaration that faith would enter the show's multiple storylines.

On the surface, there is a great deal more discussion of mere religion this year. It's driven at first by the presence of Tom Branson, the Crawleys' ex-chauffeur and new son-in-law, who is both Irish and Catholic. After being exiled for revolutionary activities in his homeland, he informs his new, culturally Anglican family that his soon-to-be born child will be christened Catholic. Meanwhile, the poor vicar is back, and he even has some lines, though in speaking them he turns out to be as much of a sop as he appeared to be when cowering before the dowager countess in Season 2—and a petulantly religious sop at that: the worst kind. There's been some debate about whether the relative agnosticism of the household is historically accurate (yes it is, say some; no, a reawakening called the Oxford Movement would have touched the place by the 1920s, say others).

Unsurprisingly, given his skill as a writer and his evident love for these characters, Fellowes proves himself largely unconcerned with such matters. To a serial novelist like him, merely religious questions are academic; it's the matters of the heart that interest him, and perhaps the spiritual matters of the heart most of all.

Is there a difference? Fellowes seems to pose the question. He finds his way further up and further in during episode 5 through Lady Sybil, Branson's wife and the youngest daughter of Lord Grantham. As Sybil is preparing to give birth, the doctors begin to argue, the women grow tense, the men withdraw, and the servants mill about downstairs under the gathering storm.

Sybil's sister, Mary, tries to comfort her, and Sybil tells her she's just realized that because of Tom's exile, the child will have to be christened at Downton.

"Blimey," Mary says.

"I wanted the whole thing done in Dublin," Sybil says. "Out of sight, out of mind. But we can't wait forever. We can't not christen the poor thing."

"You don't have to do this," Mary tells her. "It's your baby, too."

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"I don't mind," Sybil says. "I mean, I do believe in God. But all the rest of it: vicars, feast days, deadly sins—I don't care about all that. I don't know if a vicar knows any more about God than I do. And I love Tom, so very very much."

The superb actress who portrays Sybil, Jessica Brown Findlay, gives her character a deliberate and even preternatural clarity in delivering these lines, and it's as she does this that we begin to understand that Sybil will not survive the birth. We're less than five minutes into the episode.

Sybil has instinctively connected her fledgling but powerful sense of God as something, or someone, who supersedes the trappings of religion with the deep love she has for her husband. And these are the waters that British novelists Evelyn Waugh and Graham Greene spent so much time and blood mapping out.

"He can no longer have God for his father who has not the church for his mother," Cyprian of Carthage said. Fair enough—and yet it seems clear to Sybil, and to us viewers as well, that the church on offer in the world of Downton, as Fellowes has conceived it, is not a viable option for a living faith. This may be a convenience for a writer working in television these days; but it seems silly to quibble about, especially given what follows.

For the balance of the season, the brittle, petty, religious intolerances on display—especially from Lord Grantham, who finds the prospect of a Catholic granddaughter "flabbergasting"—serve to heighten the deep sense of loss in the house, upstairs and downstairs. They also set up two other major plot points, both of them rooted in the gospel.

The first is the slow restoration of Ethel, a former maid at Downton who has fallen on hard times and become a prostitute. She comes to live as a cook in the house ancillary to Downton, with Isobel Crawley, Lady Mary's mother-in-law (it's wise to watch the show with a family tree up on your laptop or iPad). Ethel's presence there is a scandal to most, though not all, of the servants and members of the Crawley family. Isobel's maid says she will be tarnished by Ethel's presence; Isobel promptly fires her. The servants of Downton are forbidden to go near the house. Mrs. Hughes, the head housekeeper, soon finds her charges' righteous indignation tiresome.

"Jesus did manage to eat with Mary Magdalene," she says, to a carping Mr. Molesley.

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"We can't be sure he ate with her," Mr. Molesley says. "He did allow her to wash his feet."

"Well," Mrs. Hughes says, eyebrows rising. "I'll tell Ethel she has a treat in store."

But Lord Grantham cannot abide this travesty any more than he can abide the Catholic one. He is outraged when the women of his house are invited to Isobel's, to be served lunch that has been cooked by a whore. He marches up to the house and demands they leave; they do not, humiliating him. Their refusal to walk out on Ethel is a kind of holy protest, a deliberate decision to forgive that resonates all the more after the mention of Mary Magdalene. I can't remember the last time I heard Mary Magdalene even mentioned on television, much less referred to in context—and with wit, no less.

The second crucial plot point that follows Sybil's death is an extraordinary and delicate minor masterpiece of writing and acting in itself: the fall, and restoration, of Thomas Barrow. Thomas' history as a gay man in the service of Downton is handled with compassion and dexterity throughout the series, and if the sentimentalism comes on a bit strong here at times, it's no more so than in other characters' arcs. In season three Thomas falls in love with the new footman at Downton, Jimmy Kent. He is cruelly set up by his enemy and sometimes ally, Mrs. O'Brien, who knows Thomas just well enough to perceive the depth of his loneliness, and eggs him on by lying about Jimmy's own feelings. Thomas finally makes an advance; Jimmy doesn't reciprocate, and Thomas is discovered and forced out of the closet. He is fired and to be sent away without a reference, therefore losing both his livelihood and the only community he has on the earth.

The believable surprise is that he is aided in the end by his oldest enemy at Downton: John Bates, who has been released from prison at last, and whose newly tested sense of justice compels him to help. Thomas is also defended by Lord Grantham, who is believably and selectively tolerant with him, and what's more is impatient with the intolerance of his staff; he sees himself in it. When Lord Grantham's judgment is questioned, he quietly asks for anyone who is without sin to cast the first stone.

In the season finale coming up Sunday, which I've seen but won't give away, these dual acts of mercy lead Thomas to a brave and heroic act of self-sacrifice, and to a genuine friendship with Jimmy that begins in one of the most moving scenes in the series so far.

Judging by the track we're on, not to mention the stupendous ratings, it would appear that Fellowes finally feels free enough to go anywhere—and a fine, fine thing that is.

This is Todd Dorman's second article about Downton Abbey for CT. He also wrote yesterday's article on Mumford & Sons.