Spiritual Union
Spiritual union stems from the relationship between Christ and the Holy Spirit given with his glorification and lying in back of that union.... Because of his resurrection and ascension, the incarnate Christ (“the last Adam”) has been so transformed by the Spirit and is now in such complete possession of the Spirit that he has “become life-giving Spirit,” with the result that now “the Lord [= Christ] is the Spirit” (1 Cor. 15:45; 2 Cor. 3:17).
Richard Gaffin, By Faith, Not by Sight: Paul and the Order of Salvation (Paternoster, 2006), 38-39.