The concept of union with Christ lies at the heart of Christian theology and is a subject I have been delving deeply into this past year. Few groups have articulated its significance as vividly as the Marrow Men, a circle of 18th Century Scottish theologians, including Thomas Boston. They were influenced by Edward Fisher’s The Marrow of Modern Divinity and championed the free offer of grace and the believer’s intimate, transformative connection with Jesus. For the Marrow Men, union with Christ was not a dry doctrine, but the very essence of salvation and the Christian life. For a fuller treatment of the Marrow Men, a good resource is Sinclair Ferguson’s The Whole Christ.

To grasp union with Christ, we begin with a simple yet profound truth: believers are “in Christ.” This New Testament phrase – woven through Paul’s letters and Jesus’ teachings – describes a spiritual bond that redefines who we are. The Marrow Men leaned on this rich, biblical imagery to bring this reality to life.

+ The Vine and the Branches (John 15:5) Jesus is the vine and we are the branches, drawing our spiritual reality from Him. Apart from Him, we can do nothing.

+ The Head and the Body (Ephesians 4:15-16) Christ is the head, directing and sustaining the church as His body, with every part united under His care.

+ The Bridegroom and the Bride (Ephesians 5:25-32) This tender love between Christ and His church mirrors the closeness of this union.

These pictures reveal that union with Christ is no mere legal transaction. It is a living, breathing relationship — organic, intimate, and life-giving. Through faith we are joined to Jesus, and in this union, we receive every blessing of salvation.

This union with Christ is a golden thread running through the gospel. Indeed, it is the gospel, the good news. Here is how this union shapes key aspects of our redemption:

Justification – When we are united with Christ, His righteousness becomes ours. On the cross, He took our sins; in exchange, we receive His perfect standing before God. Our acceptance isn’t earned — it’s a gift rooted in connection with Him.

Adoption – Union with Christ brings us into God’s family. As Jesus is the Son, we become sons and daughters, sharing His inheritance. We can cry “Abba, Father” (Romans 8:15) embraced by the same love that rests on Christ.

Sanctification – This union does not just declare us holy — it makes us holy. United to Christ’s resurrection life, we are empowered to die to sin and live for righteousness. The Marrow Men stressed that this growth in holiness flows naturally from our new identity, not from grit or guilt.

Union with Christ is the fountainhead of all spiritual blessing. It is the core of what it means to be saved.

The Marrow Men faced their share of critics back in the 18th Century and the same charges are laid against those who believe in salvation by grace alone today. They were charged with antinomianism – the notion that grace cancels out the need for obedience. After all, the critics said, if we are united with Christ and secure in His righteousness, why bother with God’s Law? The Marrow Men rightly answered their critics by insisting that union with Christ doesn’t erase the Law, it actually fulfills it.

Far from breeding lawlessness, this union with Christ ignites a desire to obey. When we taste Christ’s love and grace, we are changed from within. Obedience becomes a joyful response, not a grim duty or obligation. The Holy Spirit, working through our connection to Jesus, renews our hearts, aligning our wills with God’s will. This is the authentic path of holiness — not forced compliance but a life reshaped by love.

So, what does this mean practically? How does this truth help us live day to day. For one, it brings comfort in trials. Life can be brutal but union with Christ offers unshakable hope. If we are united to Him in His death, we will be united in His resurrection (Romans 6:5). No matter the storm, He is with us and we are secure in Him.

Secondly, it gives us assurance of salvation. Doubts may creep in, but union with Christ anchors our confidence. Our salvation rests on His finished work, not our shaky efforts. Because we are in Him, we can rest assured of God’s unchanging love.

Third, it gives us a motivation for holy living. Knowing we’re united to Christ stirs us to reflect His character. As we grasp our new identity — forgiven, adopted, empowered — we are driven to live for God’s glory, not out of fear but out of gratitude and joy.

Imagine a weary traveler, burdened by guilt and failure, suddenly finding themselves welcomed into a king’s family. That’s the daily reality of union with Christ – a truth that lifts us up and spurs us on.

As the Marrow Men rightly understood, union with Christ is the heartbeat of the gospel. It is the foundation of our salvation, the source of our growth and the comfort of our souls. This union invites us to marvel – that we, broken and unworthy, are bound to Jesus — forgiven in His death, alive in His life and destined for His glory. In a world of striving and doubt, this doctrine shines as a beacon of grace. To be in Christ is to be complete, secure and forever His. Let that truth sink in — and let it change everything.