The Trinity Visualized
This "shield of the Holy Trinity" teaches that the Father (P=Pater) is not (non est) the Son (F=Filius), the Son is not the Holy Spirit (SS=Spiritus Sanctus), and the Holy Spirit is not the Father. The Father is distinguishable from the Son, the Son is distinguishable from the Holy Spirit; and the Holy Spirit is distinguishable from the Father. However the Father is God (est Deus), nothing less, and the Son is God, nothing less, and the Holy Spirit is God, and God is essentially one.
This picture grasps the essential logic of triune teaching that avoids tri-theism, the heterodox view that Christians worship three Gods. God's unity is affirmed in three persons. God is una sabstantia, one substance, which means that God remains essentially one while becoming known in tres persona, three persons. The Father is God, the Son is God, the Spirit is God.
Quoted without parenthetical references from Thomas Oden, The Living God, 2001, Peabody, MA: Prince Press, p. 221.