Propaganda for you to make Halt O'Carrick a pagan:
OAK TREES ARE VERY IMPORTANT IN IRISH PAGNISM!!!!! Not only is the oak king associated with the yearly turn of the Wheel, but oak trees are also considered to be 1 of the 7 Airig Fedo, or Lords of the Wood, which are very valuable and spiritually important trees (no, I'm not kidding)
Halt being Hibernian (Irish) is very important to his story, which can probably go unsaid, but sometimes you have to spell things out. Why not double down on his culture? Give him an Irish accent, an Irish (birth) name, an Irish haircut, and why not an Irish religion while you're at it?
Irish chieftain and eventually kings would be sworn in underneath spiritually important trees (yeah, it's trees again), and given that Halt was an Irish king, we can assume that the Irish practices still remained. And if the Irish pagan practices remained, why not the actual Irish pagan religion?
Fun fact: Lineage was SO important in Irish tradition that, in meetings called by kings, you were not allowed to speak at all unless a bard could declare your lineage before you. So, Halt going and insulting Duncan's lineage in book 3? Way bigger deal than in canon. Like. Massively big deal.
Ogma, a god and the champion of the Tuatha Dé Danann, created the Irish alphabet Ogham because he wanted to prove he could. Come on guys, tell me Halt wouldn't love that.
C'mon. Don't be a coward. Do it. Make him pagan. I beg of you. All of you. Literally just look at a Wikipedia that's good enough
Yes I know that in Book 8 Halt was very judgemental of the people who fell for Tennysons cult, and yes I know there were very atheistic undertones to that, but come ON that's just so boringgggggggg