How do we know Jesus took away the sin of the world?

The assurance that Jesus took away the sin of the world comes from the New Testament's consistent testimony about His sacrificial work. In Hebrews 10:12, it states that Jesus offered one sacrifice for sins forever, signifying that His death was adequate to remove the sins of those He came to save. This idea is echoed repeatedly in Scripture, linking the atonement directly to the work of Christ and affirming that those for whom He died have their sins fully dealt with, as God Himself establishes the terms of salvation.