John Calvin, in Book Three of his Institutes, wrote, "How do we receive those benefits which the Father bestowed on his only-begotten Son - not for Christ's own private use, but that he might enrich poor and needy men? First, we must understand that as long as Christ remains outside of us, and we are separated from him, all that he has suffered and done for the salvation of the human race remains useless and of no value for us. Therefore, to share with us what he has received from the Father, he had to become ours and to dwell within us. For this reason, he is called "our Head" [Eph. 4:15], and "the first-born among many brethren" [Rom. 8:29]. We also, in turn, are said to be "engrafted into him" [Rom. 11;17], and to "put on Christ" [Gal. 3:27]; for, as I have said, all that he possesses is nothing to until we grow into one body with him. It is true that we obtain this by faith." (Institutes, III. I. 1.)
Most evangelicals only know the very last part: a person is saved by grace through faith; or, perhaps more simply, by faith. Despite the difficulties a mere knowledge of salvation can cause as it relates to lordship and discipleship, union with Christ stands as a doctrine for which evangelicals seem to lack knowledge of and, thereby, gain little encouragement from. Marcus Johnson, assistant professor of theology at Moody Bible Institute, wants to revive Calvin's language of union, which he considers to be the "consistent and ubiquitous refrain" in his writings (11).
One With Christ is a condensed version of Johnson's Ph.d dissertation Eating by Believing: Union with Christ in the Soteriology of John Calvin (condensed in language, not length). As an outline, Peterson discusses the biblical, theological, & historical perspectives as it relates to Calvin's understanding of union. The chapters are as follows:
The Nature of Union with Christ
Sin and the Incarnation
Justification in Christ
Sanctification in Christ
Adoption and Sonship in Christ
Preservation and Glorification in Christ
The Mystery of the Church in Christ
The Word and Sacraments in Christ
This outline gives the reader a good idea of the progression of the book as well as the movements found in Scripture. For such a dense subject from a dense writer, having such an outline is helpful. Peterson shows a great depth of interaction as he incorporates a number of historical figures as well as contemporaries such as John Calvin, Martin Luther, Augustine of Hippo, Karl Barth, D.A. Carson, and Fred Sanders. This sample represents a number of theological positions. So, while Peterson's text is largely based on Calvin's understanding, it also shows Calvin's influence on contemporary theology across evangelicalism.
Johnson has not added anything new to the discussion but has provided an accessible discussion on union with Christ. Evangelicalism seems to have forgotten the fullness of salvation that we have been given in Christ. While it may be for further discussion whether the central point to Calvin's theology was union, Johnson has given a robust discussion on the benefits of Christ from conversion to glorification. Particularly useful for many Christians today may be his discussion on preservation which entails assurance. He writes, "The gospel is full of inconceivably extravagant promises from our Father. He has given these promises to provide his children with the full assurance of his freely given, irrevocable love, and they are grounded in his steadfast, immovable, unchangeable faithfulness; what God promises he will infallibly bring to pass" (173-174).
This book may not gain popularity amongst average, Christian readers but it should. Union is an important doctrine that needs to be more fully expressed in churches. All of the benefits, even as it understand them in baptism and the Lord's Supper, come from one's union with Christ. The elevation of one's mind to think on these things (subjects with deep implications) will inevitably benefit them. Meditating on one's union with Christ, as Johnson certainly has, will lead one to worship and to walking with Christ in a worthy manner. Johnson says, "To properly understand the riches of salvation, we must grapple with this mystery" (37). Get to grapplin'.