The term means “of the same substance.” In Trinitarian theology, one divine substance exists fully and equally, or consubstantially, in three Persons. Bitter controversies arose in early Christianity concerning the divinity of the Son. The councils determined that the fullness of divinity exists not only in the Father but also in the Son and the Holy Spirit. Jesus is consubstantial with the Father and the Holy Spirit in respect to his divinity. Jesus is also consubstantial with humanity in respect to his humanity. See the Nicene Creed (BCP, p. 358) and the decree of the Council of Chalcedon (BCP, p. 864).
Glossary definitions provided courtesy of Church Publishing Incorporated, New York, NY,(All Rights reserved) from “An Episcopal Dictionary of the Church, A User Friendly Reference for Episcopalians,” Don S. Armentrout and Robert Boak Slocum, editors.