The sermon examines the spiritual danger of double-mindedness, defined as a divided heart that seeks to serve both God and the world. Drawing primarily from James 1 and 4, the text identifies this condition as an impure heart that hinders prayer and creates hostility toward God. The preacher contrasts insincere believers, who tolerate sin and lack genuine desire for holiness, with those single-mindedly pursuing the knowledge of God's will. Key indicators of insincerity include boredom in worship, rationalization of sin, and inconsistency between public faith and private life. The remedy offered is to humble oneself, mourn over spiritual adultery, and purify the heart to restore a sincere, undivided devotion to Christ.