Trinity

Yes, God is “One,” just as our Jewish ancestors taught us (Deuteronomy 6:4), and yet the further, more subtle level is that this oneness is, in fact, the radical love union betweenthree completely distinct “persons” of the Trinity. What is sometimes called the first philosophic problem of “the one and the many” is overcome in God’s very nature. God is a mystery of relationship, and this relationship is foundationally and essentially love. The three persons of the Trinity are not uniform—but quite distinct—and yet completelyoned in total outpouring and perfect receiving. 

Further, our word “person,” now referring to an individual human being, was actually first used in Greek-based Trinitarian theology (persona = stage mask or a “sounding through”), and later then applied also to us! So we also are not autonomous beings, but soundings through, seemingly separate but radically one, too, just as Father, Son, and Holy Spirit are. The implications could make for years of meditation. We really are created in God’s “image and likeness” (Genesis 1:26f), much more than we ever imagined. Trinity is our universal template for the nature of reality and for how to “one”!
By Richard Rohr