The Reformed Church in America affirms classical Nicene trinitarian theology as expressed in the Three Forms of Unity (Belgic Confession, Heidelberg Catechism, Canons of Dort). God exists eternally as three distinct persons—Father, Son, and Holy Spirit—in one divine essence or substance.

The RCA affirms the filioque clause (that the Spirit proceeds from both Father and Son) as part of its Nicene heritage, though this is stated less prominently than in the PCA. The three persons are coequal in power, glory, and eternity, sharing one divine nature while being distinguished by their personal properties and roles in the economy of salvation.

The doctrine is foundational to Christian faith and is understood to be grounded in Scripture and affirmed by the early ecumenical councils. The RCA rejects modalism and all forms of subordinationism that would diminish the full deity of any person of the Godhead.