The sermon by Brian Birdow emphasizes the importance of renouncing the past to focus on the future in Christ, drawing from Philippians 3:7-14. Paul exemplifies this by giving up his former life and achievements to pursue a greater purpose in following Christ, highlighting that believers are new creations and should not dwell on their past. The message encourages Christians to strive for their heavenly prize, illustrated as a crown of glory to be received from God.