Pastor Tyler Wittmer's sermon "Be at Peace Among Yourselves" focuses on promoting peace and unity in the church based on 1 Thessalonians 5. He highlights the importance of respecting church leaders, correcting misunderstandings about Christ's return, and actively cultivating peace within the congregation. Peace within the church is linked to honoring leaders, maintaining unity, and reflecting Christ's sacrificial love, resulting in a peaceful and harmonious community that stands out in a world marred by division and conflict.