Theodore Epp emphasizes the transformative power of tribulation in the life of a believer, encouraging Christians to rejoice in their difficulties rather than merely endure them. He explains that true joy comes from understanding that tribulations are part of God's plan to mold us into the image of Christ, as highlighted in Romans 5:3 and Romans 8:28. Epp reminds us that while tribulations are challenging, they are essential for spiritual growth and character development, ultimately leading to peace through Christ's victory over the world.