Hebrews 10:2

Hebrews 10:2. For then would they not have ceased to be offered? because that the worshippers once purged should have had no more conscience of sins.

There would have been no need to bring another lamb to be offered if the one which was presented had put away sin; there would have been no need of another day of atonement if the sacrifice on the one day had really made atonement for sin.