If this doctrine is, as John Murray wrote, “the central truth of the whole doctrine of salvation,” what does it mean and why is it so important?

First, union with Christ describes the reality of which Paul wrote in Romans chapter six. As a husband and wife are united through marriage and a parent and a child are united through birth, so we are united to Christ through the Spirit’s baptism. Those who are familiar with the historical (if not contemporary) discourses of Reformed and Lutheran preaching will immediately recognize the emphasis on the objective work of Christ in history. Themes such as election, the incarnation, the substitutionary atonement, the active and passive obedience of Christ, justification, adoption, and the objective aspect of sanctification (i.e., the declaration that we are already holy in Christ), form the diet of the best and most biblically faithful preaching. Each of these themes serves to remind the believer that his or her righteousness is found not within, but outside.

Nevertheless, there is a subjective aspect to our union with Christ which receives equal attention in Scripture and, therefore, commands equal attention from us. Calvin wrote, “We must understand that as long as Christ remains outside of us, and we are separated from him, all that he has suffered and done for the salvation of the human race remains useless and of no value for us….All that he possesses is nothing to us until we grow into one body with him” (Institutes, III.i.1).

All of our righteousness, holiness, redemption, and blessing is found outside of us–in the person and work of Christ. This was the declaration of the Scriptures and, following the sacred text, of the reformers, in the face of a subjective righteousness located in the believer. And yet, as Calvin points out, this “alien righteousness” belonging to someone outside of us would mean nothing if this righteous one remained forever outside of us. An illustration might help at this point. In my junior year of college, I went to Europe with some friends and ran out of money. Happily, my parents agreed to deposit enough money in my account to cover my expenses. Was that now my money? I had not earned it. I had not worked for it. It was not my money in the sense that I had done something to obtain it. But it was in my account now and I could consider it my own property.

While none of our righteousness is our own, Christ is! While none of our holiness belongs to us, properly speaking, Christ does!The devils know Christ is righteous, but they do not, cannot, believe that he is their righteousness.

It is essential, therefore, to point unbelievers and believers alike to Christ outside of their own subjective experiences and actions, but that is only half the story! The Christ who has done everything necessary for our salvation in history outside of us now comes to indwell us in the person of his Holy Spirit. “God has chosen to make known among the Gentiles the glorious riches of this mystery, which is Christ in you, the hope of glory” (Col.1:27). While our assurance is rooted in the objective work of Christ for us, it is also true that “We know that we live in him and he in us, because he has given us of his Spirit” (1 Jn.4:13).

John employs this language of union in his Gospel, where Jesus is referred to as a vine, with believers as branches (Jn.15). As the branch is dead apart from the life-giving nourishment of the vine, so humans are spiritually dead unless they are connected to the vine. Elsewhere, “Whoever eats my flesh and drinks my blood remains in me, and I in him” (Jn.6:56). As baptism is a sign and seal of our attachmentto the vine (the beginning of our union), the Lord’s Supper is a sign and seal of our perpetual nourishment from the vine.

Paul appeals to this doctrine as the organizing principle for his entire systematic theology. The First Adam-Second Adam contrast in Romans five depends on this notion. “In Adam,” we possess all that he possesses: original sin, judgment, condemnation, fear, alienation; “in Christ” we possess all of his righteousness, holiness, eternal life, justification, adoption, and blessing. Further, “Even when we were dead in trespasses, God made us alive together with Christ (by grace you have been saved), and raised us up together, and made us sit together in the heavenly places in Christ Jesus…” (Eph.2:5). “I have been crucified with Christ,” Paul declares, “and I no longer live, but Christ lives in me” (Gal.2:20).

Thus, this doctrine is the wheel which unites the spokes of salvation and keeps them in proper perspective. “In Christ” (i.e., through union with him) appears, by my accounting, nine times in the first chapter of Ephesians. Chosen in Christ before the foundation of the world, God has thus “made us accepted in the Beloved.” He cannot love us directly because of our sinfulness, but he can love us in union with Christ, because he is the one the Father loves. “In him we have redemption”; “in him we have an inheritance,” and so on.

Union with Christ by Michael Horton, Ph.D..