You tell people that there is One God, and then you tell them that God is One Substance with Three Persons: Father, Son, and Holy Spirit; and then you wonder why people stare blankly at you. “Trinity,” “substance” and “person” are not biblical words used to describe God. They come from the church trying to understand biblical passages that claim that the Father is God (Mtt 6:9), the Son is God (Jn 10:30; Phl 2:6; Heb 1:8; etc) and the Spirit is God (Acts 5:3). There’s plenty of NT scripture that refer to Father, Son and Holy Spirit together as if they were equal (Matt 28:19; 2 Cor 13:14; Eph 4:4-6; 2 Cor 3:16-18), but none that explain how God is still ONE while THREE.
John Wesley’s interesting Sermon 55 “On The Trinity” downplays the churches attempts to explain the Trinity through creeds and metaphors. He said,
All who endeavored to explain it at all, have utterly lost their way; have, above all other persons hurt the cause which they intended to promote; having only, as Job speaks, “darkened counsel by words without knowledge.” …I insist upon no explication at all; no, not even on the best I ever saw; I mean, that which is given us in the creed commonly ascribed to Athanasius.
Athanasius was an early 4th century bishop who famously said, “God became man that man may become God.” He cleverly and simply explained that Christ’s divinity is crucial to salvation. As a king honors all in the city where he visits, so God the Son honored all humanity by putting on flesh. Through the death and resurrection of Christ the God-man, all humanity is freed from the curse of death and able to become like God. It’s not meant to be a mathematical formula for you to just get it, it’s meant to be a mystery. It’s more important to recognize the Divinity of Christ than to try to explain how it all works. Many people won’t be satisfied with this sort of non-explanation, but when all you’ve got is metaphors to explain metaphysics, you’re sure to give yourself a meta-headache.