How do we know eternal life is guaranteed for believers?

Believers are assured of eternal life through their union with Christ, which is clearly articulated in Romans 6:3-4. This passage explains that just as Christ was raised from the dead, so too are believers raised to walk in newness of life, signifying their everlasting relationship with God. This assurance is rooted in the immutable nature of God's promises and the power of Christ's redemptive work. Believers are seen as complete in Him and assured that their lives are hidden with Christ in God (Colossians 3:3), highlighting the security they have in their faith.