Peter Brandon preaches on the theme 'What Is Wrong With the World?' using Psalm 51 as a foundation. He emphasizes that the root of the world's problems lies within each individual, as we are all born with a sinful nature. Through the story of King David's sin with Bathsheba and his subsequent confession, Brandon illustrates the importance of acknowledging our transgressions and seeking God's mercy for true restoration. He highlights that understanding our sinfulness leads to a deeper relationship with God and the joy of salvation. Ultimately, the sermon calls for personal reflection and repentance, encouraging listeners to come to God for cleansing and renewal.