William Butler Yeats lived in Ireland most of his life. Born in 1865 and dying in 1939, he was raised a Protestant in a land that was increasingly militant in its Catholicism for most of his life. He had a fascination with the occult, and with the legends of Eire. He was a skilled astrologer, and also interested in the more mystical side of Christianity.
It’s hard, therefore, to say what he believed in. The arc of his spiritual evolution is too complex, and resists easy summation.