That God is both one and many in the same moment is both incomprehensible and satisfying. His one-and-many Being grounds his goodness. God, in his unity, is never divisible except as he made space in himself at the cross for us to enter his embrace. All goes wrong if we think of him as a singular “essence” of divinity shared by a collective of three stakeholders. Instead his being as “one” is properly explained through his eternal unity of communion. In his eternal dynamism of love he is ever stable and good. That is, he is fully secure and the source of all security; and he is ever changing as one who is always creating from within the stability of his unchanging love. He is a conversation of love whose personal Word in Christ invites us to hear that love expressed in ways that are ever new.
God, in his triunity, is never alone, lonely, or needy. He enjoys, eternally, the mutual delight of his attractive otherness: of the Father loving the Son, and the Son loving the Father, each by the bonding love communicated to the other by the Spirit. God is love and his love is the bond of his oneness.
In God’s oneness there is a focus, a purpose of mutual love. In God’s triunity there is diversity and a mutual responsiveness to love. Together there is one heart, a heart that expresses itself outwardly to creation as an eternal impulse to give. This is God’s spreading goodness.