On this day atonement will be made for you and you will be cleansed from all your sins in the Lord's presents.
On the day of atonement the high priest would bake a sacrifice for the people to bring atonement. Even in the Old Testament it wasn't about what the people did or didn't do. It was about God making a way to make people right in his sight.
The interesting thing is that when the final atonement was made it was sinful gentiles who served as the priest to offer up the sacrifice that would bring atonement.