For God to be Trinity means that God explodes with delight from within. Such delight requires mutuality of persons, for it is delight at knowing and being known, delight at belonging to Another, delight at the inability of having one’s own existence apart from that Other, delight in never for all eternity having been absent from the life of the beloved Other, delight that celebrates its freedom in a playful, unstoppable dance that has as stage the whole enraptured cosmos and that thrills in abiding with the blessed Two who are Persons other than Oneself. This explosive, world-creating energy of delight wells up from the bosom of the Blessed Trinity.
What is good is “diffusive of itself”, says St. Thomas. God is too good, and therefore too “diffusive” of himself—too exuberant and squandering of his Being—to keep his secret delight to himself. The action of a divine self-outpouring is a central biblical category already at work from the first verses of Genesis: “In the beginning God created the heavens and the earth…. And the Spirit of God was moving over the face of the waters. And God said, ‘Let there be light.’” Each of these verbs—creating, moving and saying—imply a dynamic outward movement on God’s part, beyond the sphere of his own self-sufficient Being and into the void of nothingness, that he may pour himself out into what is not-God. Note the Trinitarian undertones present in Scripture from the outset: God creates not out of a splendid isolation but with the collaboration of “the Beginning, the First Principle, who says: “I was beside him as his craftsman.” The Father created all things in the Word through the Spirit. Every action of God is a self-outpouring of divine life that in no way depletes the Being of God.
The expansive throbbing of God’s triune Heart can never quite contain itself. The beaming forth of primal triune joy provides the blissful pattern for all created love and friendship. From the Trinity we learn that our own greatest joy should be to fill someone else with life.
Excerpts from Father Simeon's Homily for the Solemnity of the Most Holy Trinity.