Jessie Penn-Lewis emphasizes the centrality of the Cross in understanding the enduement of power for service in the life of a believer. She explains that many Christians seek the power of the Holy Spirit without first experiencing the deep work of the Cross and the Resurrection, which are essential for true effectiveness in witnessing for Christ. By examining the historical events of Calvary, the Resurrection, and Pentecost, she highlights that the true meaning of these events is revealed through the Apostle Paul's epistles, which provide insight into the believer's union with Christ. Penn-Lewis urges believers to seek a profound understanding of their identity in Christ, which leads to a dynamic and effective service empowered by the Holy Spirit. Ultimately, she concludes that the Cross is the foundation for unity among believers, enabling the Holy Spirit to work through them.