At a wedding recently I used these symbols to illustrate the Great Mystery (Ephesians 5) of marriage.
First the triquetra, an old Celtic symbol for the Trinity, God the Father, Son, and Holy Spirit. It also illustrates how Christian marriages invite God into our marriages, he strengthens the relationship like a threefold cord (Ecclesiastes 4)
Yet The Mystery goes much deeper:
This is The Great Mystery and Mission of marriage:
not just that we invite God into our marriages,
but that God invites us into HIS!!!