How do we know the atonement is true?

The atonement's truth is substantiated by Scripture, particularly in the context of the New Testament, where blood sacrifices of the Old Covenant are shown to be types pointing to Christ's ultimate sacrifice. It is through His death and resurrection that we see fulfilling the prophecies of the Old Testament, such as in Isaiah 53, where it foretells the suffering servant who bears our iniquities. Furthermore, the historical evidence of Jesus' resurrection serves as a powerful affirmation that His sacrifice was sufficient and accepted by God, demonstrating that we are indeed reconciled with Him through Christ's atoning work.