This sermon explores the unity of God's covenant of grace throughout Scripture, demonstrating that the Old and New Testaments share the same substance, that is Jesus Christ. It contrasts the broken covenant of works with Adam against the fulfilled covenant of grace in Christ, the second Adam, who satisfies all divine demands for His people. The preacher emphasizes that this gracious agreement is eternal, extending to a thousand generations and encompassing believers from all nations regardless of background. By examining key passages like Genesis 3:15 and Romans 5, the message highlights how Christ's perfect life and death provide complete salvation by faith alone. Ultimately, the sermon encourages believers to rest in the sufficiency of Christ and pass this enduring truth to future generations.