A.B. Simpson's sermon 'Self-Renunciation and Self-Aggrandizement' emphasizes the contrast between self-renunciation, exemplified by Gideon, and self-aggrandizement, represented by his son Abimelech. Simpson illustrates how true greatness in the Christian life comes from serving others rather than seeking personal glory, warning against the dangers of pride and ambition that can corrupt even noble endeavors. He draws parallels between the destructive nature of selfishness and the ultimate sacrifice of Christ, urging believers to embrace a life of selfless love and service. The sermon concludes with a call to allow Christ to live through us, transforming our lives from self-centeredness to selflessness.