'The Gospel Mystery of Sanctification' by Walter Marshall, first published in 1692, is one of the classic works of Christian spirituality. It is a deep and rich biblical study of sanctification - how Christians grow in holiness and become more like Jesus. In a day when Christians are very prone to pursue self-help methods to grow in obedience to Christ, Walter Marshall lays out the biblical way of growth: obedience comes as Christians live by grace, in union with Christ, by faith. Growth comes, as Paul says in Galatians 2:20, through "Christ living in me." The message of thibook is so important for Christians today, it is essential that it be rewritten in contemporary English.