How do we know the importance of Christ's perfect life for believers?

The sermon emphasizes that the only source of true warmth for our hearts comes through the perfect life of Jesus Christ. Just like King David relied on the young virgin for warmth, believers rely on Christ's sinless life for their righteousness before God. The preacher states that all human efforts to gain God's favor are like filthy rags and insufficient for warmth, underscoring the necessity of Christ's work for salvation and sanctification. In union with Him, we share in His life, death, and resurrection, giving us hope and assurance.