As Christians, we know we’ve been saved by Christ, we should look like Christ, and we can have a relationship with Christ. But we rarely consider how all this depends on our union with Christ.
The whole of our salvation can be summed up with reference to this reality. Union with Christ is not a single specific blessing we receive in our salvation. Rather, as Michael Horton points out, it is the best phrase to describe all the blessings of salvation, whether in eternity (election), in history (redemption), in the present (effectual calling, justification, and sanctification), or in the future (glorification).
Every blessing is received “in Christ” (Eph. 1:3). No part can be excluded from our union with him. This is the foundation and basis for all his gifts. So while it’s appropriate for theologians to talk about an “order of salvation” (ordo salutis) whereby we are called by the Spirit, born again, moved to faith and repentance, justified, adopted, sanctified, preserved, and glorified, we must never separate these benefits from the Benefactor. Every blessing in the order of salvation flows from our union with Christ. As John Murray said, “It is not simply a step in the application of redemption; when viewed, according to the teaching of Scripture, in its broader aspects it underlies every step of the application of redemption. Union with Christ is really the central truth of the whole doctrine of salvation not only in its application but also in it once-for-all accomplishment in the finished work of Christ.”
The doctrine of union with Christ is so common in the New Testament that it is easy to miss. Over two hundred times in Paul’s letters and more than two dozen times in the writings of John we see expressions like “in Christ,” “in the Lord” or “in him.” We are found in Christ, preserved in Christ, saved and sanctified in Christ. We walk in Christ, labor in Christ, sorrow in Christ, and conquer in Christ. We obey in Christ and are made perfect in Christ—just to name a few examples. Another thirty-two times Paul speaks of believers participating together with Christ in some aspect of redemption, whether it’s dying with Christ, being buried with Christ, being raised with Christ, or being seated with Christ.
Apart from this kind of union, all the blessings of Christ would be outside us. It’s only when the Spirit joins us to Christ and we are ingrafted into his body that we can participate, not only in Christ’s benefits, but in Christ himself. The whole of the Christian life from election to justification to sanctification to final glorification is made possible by, and is an expression of, our union with Christ. That’s why Jesus’ final request in the High Priestly Prayer is that “I [may be] in them” (John 17:26) and why Paul says “Christ in you” is the hope of glory (Col. 1:21).