Union with Christ is not a sentiment, metaphor or illustration, or even primarily a “doctrine”. Nor is it a way of speaking about something else—whether justification, sanctification, or any other benefit of Christ (even if it includes all of these and more!). Our union with the living Christ is the essential truth of our new and eternal existence.
1. The Bible contains an astonishing number of terms, expressions and images that bear witness to the reality of our being made one with Christ Jesus.
In the Newer Testament we find literally hundreds of references to the believer’s union with Christ. To cite merely a few examples, believers are created in Christ (Eph. 2:10), crucified with him (Gal. 2:20), buried with him (Col. 2:12), baptized into Christ and his death (Rom. 6:3), united with him in his resurrection (Rom. 6:5), and seated with him in the heavenly places (Eph. 2:6); Christ is formed in believers (Gal. 4:19) and dwells in our hearts (Eph. 3:17); the church is the body of Christ (1 Cor. 6:15; 12:27); Christ is in us (2 Cor. 13:5) and we are in him (1 Cor. 1:30); the church is one flesh with Christ (Eph. 5:31–32); believers gain Christ and are found in him (Phil. 3:8–9).
Furthermore, in Christ we are justified (Rom. 8:1), glorified (8:30), sanctified (1 Cor. 1:2), called (1:9); made alive (Eph. 2:5), created anew (2 Cor. 5:17), adopted (Gal. 3:26), and elected (Eph. 1:4–5). Whew! All this without reference to the Gospel and letters of John! Suffice it to say, union with Christ is an absolutely fundamental gospel conviction of the Apostles—dear to them because it was so dear to their Lord.
2. When we are joined to Jesus, we are included in the greatest mystery of the universe—the incarnation of God.
C.S. Lewis calls the incarnation of God the Son the “central miracle” of Christianity. He is right. The redemption, restoration, re-creation, and reconciliation of sinners—and all of creation besides—depends entirely on the supreme fact that God, without ever ceasing to be fully who he is, became fully who we are in and as Christ Jesus. Why did God do this? Why is it, in other words, that the “Word became flesh”? The principal reason underlying all the other magnificent reasons that God the Son united himself to our humanity is this: that by the Holy Spirit we may be united to Christ and so enjoy his fellowship with the Father forever. This is eternal life (John 17:3).
3. Our union with Christ is profoundly real and intensely intimate.
Union with Christ is not a sentiment, metaphor or illustration, or even primarily a “doctrine”. Nor is it a way of speaking about something else—whether justification, sanctification, or any other benefit of Christ (even if it includes all of these and more!). Our union with the living Christ is the essential truth of our new and eternal existence. In a way that gloriously transcends our finite understanding, we are really and truly joined—spiritually and bodily—to the crucified, resurrected, incarnate person of Christ. There is no better news than this.
4. Because union with Christ is so central to the gospel, it has resonated in the teaching and preaching of the Church throughout the ages.
Unsurprisingly, given the ubiquity of the theme in the Scriptures, there is a massive chorus of churchly voices who have emphasized the significance of being united to Christ. This historic theological chorus includes the likes of Irenaeus, Athanasius, Augustine, Cyril of Alexandria, Bernard of Clairvaux, Martin Luther, John Calvin, John Cotton and Jonathan Edwards (to name but a few).
According to Calvin, our union with Christ is to be accorded “the highest degree of importance.” Why? Because being joined to Jesus is the whole point of the gospel: “For this is the design of the gospel, that Christ may become ours, and that we may be ingrafted into his body.”
5. Justification is a magnificent benefit of being united to Christ.
We are not united to Christ because we have been justified. It is quite the other way around: we are justified because we have been united to Christ, who is himself our justification (1 Cor. 1:30). We receive Christ’s benefits precisely and only because we receive Christ. Martin Luther knew this well: “But so far as justification is concerned, Christ and I must be so closely attached that He lives in me and I in Him. What a marvelous way of speaking! Because He lives in me, whatever grace, righteousness, life, peace, and salvation there is in me is all Christ’s; nevertheless it is mine as well, by the cementing and attachment that are through faith, by which we become as one body in the Spirit.”