The little intruder wasn't even baptized yet: the newborn daughter of the (late) Lady Sybil and her husband, the former chauffeur, the Irish Mr. Branson.
Here's the back story, in case you missed it:
After the funeral, the Earl's family mentioned that they really ought to see about the child's christening. At the mention of Mr. Travis, the local clergyman, the young father spoke up. The baby, he said, is Irish. She will be Catholic. It's just part of being Irish--or perhaps to the revolutionary Mr. Branson, it is another way of not being English.
All in all, a conversation among agnostics about which church offered more appropriate social benefits for the newborn: Catholic (in line with her ethnic and national identity as Irish, since she would in fact be raised by her father) or Anglican (to assure her place in high society as a descendent of the house of Grantham). Even the late, lamented Lady Sybil had already mentioned to her sister that the baby would be raised Catholic for her father's sake, and not because Mr. Travis or anyone else knew more about God than the next person. Post-modernists before the fact!
It's rare enough that the very issue would be raised in a high profile TV series, so I was glad to see this in the program, along with the dismissive remarks of the Earl about his grandchild being a "left-footer" and the comment about there having been no Catholic Crawleys since the Reformation (when the imaginary Downton Abbey would have been seized from the monks or nuns who built it and given to the politically connected). I also enjoyed the hint of rebellion in the Dowager Countess' (Maggie Smith's character) expression of high esteem for the Dowager Duchess of Norfolk (read between the lines: the Duke of Norfolk was alone in the realm in not accepting the Church of England back in Elizabethan days).
So the conversation wasn't very substantive, but this is TV! At the very least, it shows that being Catholic was then, as now, a sign of contradiction. (Are we worthy of that?)