The letter of Philippians is a New Testament epistle written by the apostle Paul while in prison. It encourages the Philippian church in the joy of Christ, urges them to live in unity and humility, and emphasizes the importance of Christ's sacrifice and the Christian's responsibility to continue in that same selfless spirit. Key themes include the nature of Christ as Lord and example, the fullness of God's power and provision, and the hope of eternal life through faith in Christ. Concisely summarized, Philippians is a call to live out the Gospel of Christ with joy and humility, trusting in His power and provision.