Abstract
This study proposes to draw up a synthetic inventory of the Paulinian expressions of the so called to be in Christ in order to underline the essence of the Christian mystic life. The Paulinian expressions: in the name of Christ, through Christ, in Christ, of Christ, with Christ testify a mystic relation between Christ and His believers. There is an obvious parallelism between the affirmation upon Jesus Christ and the one upon Holly Spirit in the Christian living. Our approach tries to specify what is the meaning of the mystic union with Christ. This is a point of view based upon the Christocentric and Trinitarian mystics, ensuring the ontological plenitude of the human essence, through the permanent participation to the Christian life. These Paulinian expressions gathered around the syntagm of being in Christ are the sublimations of the Christian modus vivendi for which the mystic union with Son of God is accomplished through the Trinity.

Keywords
Christ, union, love, being, death.