This book revolves around the need for reliance on the Holy Spirit, as well as the need for believers today to seek the Spirit of God for the fullness of power. In this book, Moody distinguishes between the Spirit "in" a believer at conversion and the Spirit resting "upon" them in power for service. He examines how the Holy Spirit empowers a believer as well as some of the obstacles to His work. The subjects touched upon are: Power — It's Source - Power "In" and "Upon" - 

Witnessing in Power - Power in Operation - Power Hindered