What is the most important book on sanctification? For John Murray, it was Walter Marshal’s The Gospel Mystery of Sanctification. William Cowper praised Marshall: “I think Marshall one of the best and most spiritual expositors of Scripture.” The Marrow men also commended Marshall. Even Andrew Murray believed Gospel Mystery to be “the one book . . . admitted by all to be the standard on sanctification.” Marshall’s enduring value is well established, yet scarcely any resources explain Marshall’s theology. T. Michael Christ’s A New Creation in Christ fills this void by exploring Marshall’s theology in the context of the antinomian and neonomian controversies of Marshall’s day. At a time when interlocutors where pushing one another to further extremes, Marshall achieves balance because he grounds sanctification in the believer’s union with Christ and deploys two limiting concepts that discourage using one error to refute the other. He insists both that some measure of assurance of salvation must precede actual works of holiness (refuting neonomianims) and that holiness is a necessary part of salvation (countering antinomianism). A New Creation in Christ explores how these limiting concepts translate into practical help for those who, as Marshall says, pursue holiness “under the guilt and power of indwelling sin.”