A.B. Simpson emphasizes the supernatural nature of faith and the necessity of complete dependence on God, as exemplified by the Israelites in the wilderness. He argues that true strength comes from the presence of God, not from human resources or wisdom, and that a church must rely solely on divine power to fulfill its mission. Simpson highlights the importance of recognizing God's presence as the source of grace and strength, urging believers to embrace the transformative power of the phrase 'But God.' He calls for a reliance on the Holy Spirit to understand and embody this truth in their lives.