The doctrine of union with Christ is the biblical reality that a believer is joined to Christ in an intimate and mysterious way. Since Christ is the source of living for the Christian, union with Christ is essential for salvation, abundant life, and growth in Christ-likeness. In the gospel, we are in Christ and Christ is in us (2 Cor. 13:5, 1 Cor. 1:30). All of the blessings of the gospel flow from our union with Christ.
The Bible uses a number of different phrases for this reality. We are created in Christ (Eph. 2:10), crucified with him (Gal. 2:20), buried with Christ (Col. 2:12), baptized into Christ (Rom. 6:3), united with Christ in his resurrection (Rom. 6:5), and seated with him (Eph. 2:6). The Bible also describes the blessings of our salvation that are ours in Christ: Election (Eph. 1:4-5), justification (Rom. 8:1), adoption (Gal. 3:26), sanctification (1 Cor. 1:2), coming to spiritual life (2 Cor, 5:17), and glorification (Rom. 8:30).
The above passages, and many more in the New Testament, show us that the Christian Life is entirely dependent upon our union with Christ. To live the Christian life without union with Christ is like trying to turn on a lamp without plugging it into a power source. It will not work.
Union with Christ should lead us to thankfulness to and worship of Christ, the fountain of every blessing. If we are not united in Christ by faith, we have no claim to any of the blessings of God. But in Christ, we have been blessed with every spiritual blessing in the heavenly places (Eph. 1:3). Union with Christ is also key to our sanctification. All of the resources we need for practical Christian growth and living are found in Christ (Phil. 2:5). Jesus says that we can do nothing apart from him (John 15:5).
This truth also leads us to loving engagement with fellow believers who are also united to Christ and make up the body of Christ. Our union with Christ means we are a part of the family of believers, the church. Union with Christ also gives us assurance and encouragement when we are burdened by struggle. We did nothing to get ourselves in Christ, and Christ will not allow anything to snatch us out of him (Jn. 10:28).
While there are many more benefits of union with Christ, Charles Spurgeon summed up the blessing of this truth well when he said, “There is no joy in this world like union with Christ. The more we can feel it, the happier we are.”