The triquetra, also known as the trinity knot,as been used in ancient Nordic, Celtic, German, and Japanese cultures. It has been used in both pagan and Christian religious imagery as well, symbolizing the Holy Trinity in the latter.
“I must not fear. Fear is the mind-killer. Fear is the little-death that brings total obliteration. I will face my fear. I will permit it to pass over me and through me. And when it has gone past I will turn the inner eye to see its path. Where the fear has gone there will be nothing. Only I will remain.”
― Frank Herbert, "Dune"