How do we know Jesus' atonement is true?

We can trust in the truth of Jesus' atonement because it is deeply rooted in Scripture and fulfills God's redemptive plan foretold throughout the Old Testament. He became sin for us, taking on our iniquities, which is confirmed in passages like Isaiah 53. His cry of 'It is finished' from the cross signifies the completion of the work He accomplished. Furthermore, Jesus' own assurance, 'Father, of all that thou hast given me, I have lost none' (John 6:39), emphasizes the security of those who are redeemed. The distinction made in Scripture between the elect and the reprobate also solidifies the assurance that His atonement is effective for those whom the Father has given Him.