The opening volume of Gurnall's three-part exposition of Ephesians 6:10-20, covering the Christian soldier's call to be strong in the Lord and the general nature of spiritual warfare. Gurnall establishes the framework that governs the entire work: the Christian life as a sustained combat against sin, Satan, and the world, requiring both divine armor and active use of it.

The second volume continues the exposition through the belt of truth, the breastplate of righteousness, and the preparation of the gospel of peace, each receiving extended treatment. Gurnall's method combines close exegesis of the apostle's imagery with searching application to the practical experience of the Christian under trial and temptation.

The concluding volume covers the shield of faith, the helmet of salvation, the sword of the Spirit, and the long discourse on prayer that carries the exposition through to the close of the epistle. Together with the first two volumes it forms one of the longest and most celebrated works of Puritan practical theology, admired across centuries for the depth of its pastoral application.