Book of Philippians Summary: Joy in Christ Amid Chains. The letter to the Philippians is often called Paul’s “letter of joy,” but that joy is no shallow optimism. It was written from prison, under chains, with the real possibility of death ahead. Despite those circumstances, Paul presents one of the most uplifting and Christ-centered writings in the New Testament. Philippians reveals what true Christian joy looks like: not rooted in circumstances, but in Christ Himself.