How do we know the atonement of Christ is sufficient?

Christ's atonement is deemed sufficient because it is not just a cover for sin but a complete removal and payment for our transgressions. In the book of Leviticus, we see that sacrifices were to be fully consumed, symbolizing that Christ's sacrifice was total and complete. As stated in the sermon, 'there is no atonement made unless there's a variance'; thus, Jesus' sacrifice satisfies the justice of God, making Him our propitiation. This means that not only does He take away our sin (expiation), but He also restores our friendship with God, making us His children, as expressed in Matthew 26:28 where He states His blood is poured out for many for the forgiveness of sins.