How do we know the doctrine of Christ's eternal salvation is true?

Hebrews 5:9 states that Christ became the author of eternal salvation to all who obey Him, highlighting that His sacrifice fulfills God’s redemptive plan. This underscores the belief that salvation is not temporary; it is an eternal promise to those who genuinely submit to Christ. Furthermore, Christ's uniqueness as both God and man validates this doctrine, enabling Him to take on the sins of humanity and offer a perfect sacrifice. This is key to understanding that genuine faith in Christ secures eternal salvation, as it is reliant not on human efforts but on His perfect obedience and sacrificial love.