One-Inness in Christ

The word Christian, while meaning many things to many people in our modern world, has one essential meaning: "to be in union with Christ." The apostle Paul repeatedly uses the term "in Christ" in the introductions to his letters to the Romans, Thessalonians, Colossians, Philippians, and Ephesians, where the doctrine of union with Christ is plainly evident. These greetings highlight the truth of Christ's incarnation and His indwelling presence in believers. John Calvin captures this, stating, "We do not, therefore, contemplate him outside ourselves from afar in order that his righteousness may be imputed to us but because we put on Christ and are engrafted into his body—in short, because he deigns to make us one with him" (Institutes of the Christian Religion, Book III, Chapter 2, Section 24). In the reality of union with Christ, we find the external work of His incarnation. This work is applied internally to us through the Holy Spirit, what we have termed "one-inness in Christ," the center of our salvation and sanctification. The New Testament provides four metaphors to understand this mystery: marriage, the body, the temple, and the building. In our modern day, Louis Berkhof has perhaps phrased it best: "That intimate, vital, and spiritual union between Christ and His people, in virtue of which He is the source of their life and strength, of their blessedness and salvation" (Systematic Theology, Louis Berkhof).