In this sermon from Grace to You, John MacArthur analyzes Peter’s denial (Mark 14:66-72) as a warning against spiritual overconfidence. Peter’s failure demonstrates that even dedicated believers can fall when trusting in their own strength, rather than relying on God.  MacArthur urges believers to reject self-confidence, stay vigilant, and rely solely on divine strength for spiritual victory, acknowledging that without God, we are all capable of serious sin.