We celebrate the feast of Trinity Sunday as the mystery of the Three divine Persons in one God – a mystery totally above or comprehension, explained by St. Patrick by the example of a clover leaf, with three parts, yet still one leaf.  Or a triangle … one figure with three different sides.  Jesus speaks of His Father as a separate Person, and refers also to the Holy Spirit, so He Himself provides us with this small detail of the mystery.  A mystery is something which is beyond our human reasoning.