John Arnott MacCulloch, a Scotsman, was born in 1868 and died in 1950. He was one of Scotland's most famous Celtic Scholars and folklore researchers and he published The Religion of the Ancient Celts in 1911 and his lengthier The Mythology of All Races (in thirteen volumes, published in 1918).
According to Chebucto Community Net, he wrote The Religion of the Ancient Celts during a long residence in the Isle of Skye, a place MacCulloch claimed to be "easier to attempt the ancient religion than in a busier or more prosaic place" because it "is where the old language of the people still survives, and where the genius loci speaks everywhere of things remote and strange."
MacCulloch's book became an instant classic as it was one of the first to attempt to rebuild Celtic paganism and postulate its inner spirit. MacCulloch portrays the Celt as a seeker after God, linking himself by strong ties to the unseen and eager to conquer the unknown by religious rite and magic art. The earliest aspect of the Celtic religion, MacCulloch believed, was the cult of nature spirits and of life manifested in nature.