Trinity Sunday is the only festival on the liturgical calendar dedicated to a doctrine and not a very easy one to understand at that. It was a hot topic in the fourth century, especially for those on the losing side of the conversation, but then the teaching of the unity of Father Son Spirit has been a major source of division, most famously the break between the Eastern and Western church in 1054. Today we confess the creed without much thought to the difficulty of defining three persons with one essence though this Sunday preachers will try to explain the mystery in such a way as to make it less mysterious, while hopefully avoiding any number of heresies. At Calvary we make our interns preach on Trinity Sunday just in case they are heretics in pastor clothing. Maybe letting the mystery of Father Son Spirit remain unexplained is the best way to celebrate the God beyond knowing whose unconditional love is revealed in creation and cross and confession of faith.