My ancestral lineage can be traced back to Scotland during the Scottish Wars of Independence, all the way to the gruff Picts and so on. This is interesting to me, though the term "Celtic" pertains mostly to Irish cultures, while Scotland is generally more Gaelic... though the Gaels are a subgroup of the Celts so I guess it doesn't matter. My direct family is mostly Fundamentalist Christian, and they sprung from their Presbyterian origins from Scotland after the reformation.
Honestly, I haven't heard of many people delving into the celtic religions, though they are quite fascinating and refreshing in comparison to the mainstream monotheisms. Inevitably, even those who are monotheistic have their own subjective visages of God, so even they are polytheistic if you think about it, especially when you see that Catholicism venerates saints as if they are gods themselves. And of course, the "trinity" is a scattershot God that diverges in a kind of polytheistic way.
And since people have their own interpretations of God, it's only fitting that the farmer prays to the god of the harvest, and the general prays to the god of war, and each one prays for their own sake. I wonder why.