In recent decades, the theme of ‘union with Christ’ has experienced a notable resurgence within Protestant theology, emerging as a central motif for rearticulating key doctrines of salvation, sanctification and ecclesiology. This renewed interest responds to earlier tendencies, especially within post-Reformation scholasticism and modern evangelicalism, that had fragmented soteriology into discrete stages of an ordo salutis, such as justification, regeneration and sanctification. Contemporary theologians have instead emphasised the participatory dimensions of salvation, arguing that union with Christ functions as the ontological and relational foundation for all aspects of the Christian life. In the 1980s, the so-called Finnish Interpretation of Martin Luther presented a then-radical thesis along the aforementioned lines. Since then, the thesis has become significantly less shocking. Contemporary Reformed theologians such as J. Todd Billings, Michael Horton and Carl Mosser have drawn on both Reformed and patristic sources to recover the relational realism of this theme, positioning it as a corrective to overly forensic or solipsistic interpretations of justification.
Moreover, this renewed focus has sparked ecumenical and interdisciplinary conversations, particularly in relation to Eastern Orthodox notions of theosis and contemporary discussions of embodiment and identity, suggesting that the recovery of unio cum Christo offers a more holistic and transformative vision of Christian existence. One illustration of the mainstreaming of this idea is the recent Oxford Handbook on Deification, an immensely valuable resource for understanding the issue more deeply and with nuance.
In keeping with this ecumenical trend, Fred Sanders argues that the doctrine of union with Christ is central to understanding the entire structure of Christian theology and spirituality. He presents union with Christ not as one obscure (or even slightly suspicious) doctrine among others but as the integrating reality that connects the believer’s salvation, sanctification and eschatological communion with God. For Sanders, this union is fundamentally trinitarian and rooted in ancient creeds: believers are brought into fellowship with the Father through the Son by the power of the Holy Spirit. He insists that this participatory union is not merely existential, metaphorical or ethical but a real participation in Christ’s life, death and resurrection – the means by which believers share in divine life without erasing the Creator–creature distinction.
The opening chapter, ‘The Creed in Christ’, demonstrates how the church’s early creeds imply and teach participation in Christ’s life, death and resurrection. In ‘Scripture in Christ’, Sanders grounds the idea biblically, particularly in Paul’s use of the phrase ‘in Christ’, arguing that salvation is not merely legal or moral, but relational – a transformation rooted in sharing Christ’s own life through the Spirit. ‘Variations on a Soteriological Theme’ surveys the history of the doctrine from the early church to the Reformation, revealing that despite differing emphases, Christian theology has consistently understood salvation as participation in divine life. Here, one notices how Sanders draws from older Reformed divines, many of whom are less well known to modern audiences, or even to theologians outside the Reformed tradition. This helps him establish his thesis, according to which union with Christ is not a bizarre and new theological invention, but rather something well presented in the tradition. In ‘Union with Christ as Trinitarian Soteriology’, Sanders highlights that this union is inherently trinitarian: believers are united to the Son, reconciled to the Father, and indwelt by the Spirit. The final chapter, ‘Union with Christ and the Christian Life’, applies this vision to daily faith, showing how it shapes moral action and community life. He frames union with Christ as both the source and the goal of Christian existence: the ground of justification and sanctification, and the means by which believers come to truly ‘participate in divine nature’ (2 Pet. 1:4).
According to Sanders, union with Christ offers a properly theological framework for soteriology and all salvific actions of God towards humankind, creating a coherent picture of the divine economies. However, his study also highlights a set of new issues that require further theological consideration. I understand that Sanders’ work is not intended to discuss these in detail, but nonetheless, it is good to look ahead to where the discussion should move next. The topics include, for example, the following: What kind of role does the union with Christ play for sacramental theology, ecclesiology and the doctrine of ministry? How should we understand the relationship between human and divine agency (especially creaturely activity and passivity) before and after conversion? Is some form of compatibilism inherent in this way of thinking?
Union with Christ is a rare theological work that combines profound doctrinal insight with exceptional clarity and accessibility. Sanders writes with precision and warmth, presenting a deeply trinitarian vision of salvation that is both intellectually rigorous and pastorally rich. This book is particularly valuable for clergy seeking to deepen their preaching and teaching on the meaning of salvation, but it is also equally rewarding for informed lay readers who wish to grasp the heart of the Christian faith in a fresh and insightful way. Ultimately, the book functions as a retrieval of classical Protestant and patristic insights, inviting contemporary theology to rediscover the richness of salvation as participation in the triune God through Christ.
