Pewter Brooch in Trinity Knot with Border design. Legend: Trinity Knot (Triquetra) is the simplest of Celtic Knots symbolizing a triune God. For the Celts everything came in threes, maid, mother, crone & the three elements: earth, fire and water. Christianity embraced this knot to symboilize the Father, Son and Holy Spirit in many of the early Christian illuminated manuscripts such as the Book of Kells. The use of the Trinity Knot in jewellery design is associated with eternity and eternal love.