The central doctrine in James Relly’s theology was the belief that Christ is to His Church in such a whay that Christians have already died with him on the cross. Everything that can be said about Christ can also be said of those who are united with him. The Church has died with Christ and has been made righteous by Christ alone. This is union is eternal as a result of election, and realized in the incarnation. Faith is not the condition of union with Christ, but a knowledge of this union and one’s identity in Christ.
Relly developed this idea in his Union: or, a Treatise of the Consanguinity and Affinity between Christ and his Church from 1759. The idea later became pivotal in the development of Relly’s universal eschatology, as he came to believe that the whole humankind was united to Christ in this way.
“From the Grace and truth of Union, the Christian hath a right to reckon of Himself, of his state, and condition towards God, according to Christ; according to the state and Condition which He is in: hence saith the Apostle, reckon ye yourselves to be Dead indeed unto sin, but alive unto God through Jesus Christ our Lord (Rom. 6:11).”
Download: Union: or, a Treatise of the Consanguinity and Affinity between Christ and his Church (edition from 1812) (pdf)