If there is a single element that defines the belief system of the Celts (pronounced with a hard K as in "Kelts", not with a soft S as in "Selts") it is the worship of the Goddess. From the earliest times of Celtic ancestry - 35,000 years ago - up until the advent of Christianity, the central spiritual theme throughout the world was reverence for the Goddess, the Giver of Life, the Earth Mother. No male deity has equaled her power or benevolence, and none is likely to for She is our Mother who nurtures and comforts us, and who opens the door for our entry into this life.
She is most powerful in Her Triple Form - as maiden, mother and crone - as She addresses our needs in every phase of our life. The Celts called her Brigit or Bride and the Christians call her St. Bride. She is also known as Arianrhod and Hecate and we see the manifestation of the Triple Goddess in every Moon cycle. The New Moon is the Maiden Moon, and she follows her consort the Sun very closely, rising during the daylight hours. As she matures, she becomes the Mother Moon or Full Moon, pregnant with possibilities. And in her old age she is the Crone Moon, wise and independent, powerful in her own right, she leaves the daylight to the Sun and sends her energy to us only during the night. At the time of the Christian Diaspora, the Goddess was found to be inconsistent with Christian beliefs, although She remains a major part of Catholicism in the form of Mary. We don't know exactly what the early Christians were thinking when they killed the Goddess, but we do know that they have succeeded in demonizing Her in various ways.
The Triple Goddess has been replaced by the modern patriarchal triumvirate of Father (in place of Mother), Son (in place of Maiden) and Holy Ghost (in place of the magical, mystical Crone). The Crone was so powerful and mysterious that only an intangible concept like the Holy Ghost could replace Her. But Her symbol need to perish according to the philosophy of the time, and we don't have to search far to find examples of the denigration of the Crone. Once considered wise, powerful, beneficent and even beautiful in her age, she is now the Hag, the Witch, the frightening figure of danger in our Fairy Tales. The classic death blow to the Goddess, however, comes in the Book of Genesis. Here She is given the burden of the Downfall by tempting Adam and causing their ultimate expulsion from Eden.
Most of the earliest permanent art is symbolic of the Goddess, from the 30,000+ year old Venus of Willendorf and the Goddess of Lespugue to the cave paintings of Cro-Magnon and Neanderthals, we see the Goddess everywhere. In fact, the caves themselves are symbolic of the Womb of Earth Mother. When the ancestors of the Celts moved out of the caves and began farming, they continued to build cairns and megaliths, which are representative of our Mother's womb. Many of these cairns are designed with a long central hallway that is positioned in such a way that the Sun's rays at dawn on the Winter Equinox shine all the way to the end of the hall. This symbolizes the penetration and impregnation of Earth Mother by the Sun and guarantees fertility for humans and all other living things on the Earth. We may never know all the myriad ways the Celts and their ancestors honored the Goddess, but we are absolutely sure they did. Some scholars are now saying that Stonehenge was built by the Celts as a birthday present to Earth Mother; an idea that seems to be infused with the kind of magic indicative of early Celtic life. Whether we ever decipher the symbology of those who came before us or not, the fact remains that the Goddess was never really killed by the Christians. She has merely been in hiding and She is now returning.