On the Tri-Circle (Triquetra)
This symbol is of Celtic origin.
The triquetra is often found in Insular (Celtic) art, most notably metal work and in illuminated manuscripts like the Book of Kells. It is also found in similar artwork on Celtic crosses and slabs from the early Christian period. The fact that the triquetra rarely stood alone in medieval Celtic art has cast reasonable doubt on its use as a primary symbol of belief. In manuscripts it was used primarily as a space filler or ornament in much more complex compositions, and in knotwork panels it is a design motif integrated with other design elements. Celtic art lives on as both a living folk art tradition and through several revivals. This widely recognized knot has been used as a singular symbol for the past two centuries by Celtic Christians, and by Pagans and agnostics as a sign of special things and persons that are threefold.
Only since the 19th century has the triquetra found a place in Trinitarian theological symbols. However, it falls short of being a representation of the trinity. One should compare it to the three interlocking circles that does, in point of fact, represent the Trinity.
The triquetra is a circle that has been tri folded.
When I teach about the omnipresence of God I say: God is a circle Whose center is everywhere and Whose circumference is nowhere.
Then, when I teach about the economy of deity, I tri-fold the circle to represent the Father, Word/Son, and Holy Spirit - notice that while the tips of the symbol are separate (demonstrating the distinction between the offices/manifestations/modes) they are all three the same circle; notice that at the center the Father, Word/Son, and Holy Spirit are all three the same individual. In this sense the One God arranges His deity into an economy to facilitate redemption. This configuration is not eternal. God has not always existed in the modes of Father, Word/Son, and Holy Spirit (these modes are necessary to redeem a fallen creation). Furthermore, when the restitution of all things is accomplished the economy of deity will unfold back into the Circle, Whose center is everywhere and Whose circumference is nowhere.
Trinitarians think the triquetra represents a Trinity; however, the triquetra does not adequately represent three separate and distinct persons - as does the three interlocking circles. This fact is an aid in their evangelization, however. The triquetra brings the truth of the Godhead into sharp focus and is used by those Trinitarians who, in truth, are Modalist but are still using a Trinitarian vocabulary. As I pointed out above, it teaches Modalism much better than it teaches the Trinity.
It is correct that most today see the triquetra as a recent Trinitarian symbol; although it is very ancient in the Church. For example the triquetra was used by the Celtic christians in the early centuries of Christianity as a decorative Celtic knot. It is doubtful that the triquetra was used by the Celts to represent the Godhead because it is never seen standing alone. The Celts may have used the term Trinity but were by-and-large Modalist. It must be pointed out that Sabellius, himself, used the word Trinity to describe his form of Modalism. The triquetra, however, has only been used to represent the Trinity for the last 200 years; which represents how the view of the Godhead is becoming more and more Modalistic among those who still consider themselves Trinitarians..
Some say it is a pagan symbol and should be rejected as having no Christian merit. Other persons would be just as adamant that the cross is evil because it was a symbol used in paganism before it became popular in Christianity. IMHO, a symbol can stand for anything one wants it to stand for. A symbol may represent different things to different groups: e.g. I may employ the rainbow as a covenant symbol, while the gays employ it as their symbol, and Jesse Jackson uses it in yet another way. There is nothing intrinsic in any particular symbol that makes it good or evil - it is the explanation that is put on it. A symbol only has valid meaning within the particular community that is using it.
That the Oneness think the triquetra represents a Trinity of persons only demonstrates how badly we need educated.