A.W. Tozer emphasizes that Christian leaders are not independent agents performing God's work but rather obedient instruments through whom God accomplishes His purposes. He clarifies that while believers are called to labor in the Lord, it is essential to recognize that their efforts are empowered by God's grace and energy. Tozer cites 1 Corinthians 15:58 and Colossians 1:29 to illustrate that true labor in the Lord is not in vain, as it is God who works through us. The sermon encourages believers to fully commit to their calling, understanding that their work is a partnership with God.