The old system under the law of Moses was only a shadow, a dim preview of the good things to come, not the good things themselves. The sacrifices under that system were repeated again and again, year after year, but they were never able to provide perfect cleansing for those who came to worship. If they could have provided perfect cleansing, the sacrifices would have stopped, for the worshipers would have been purified once for all time, and their feelings of guilt would have disappeared.
But instead, those sacrifices actually reminded them of their sins year after year. For it is not possible for the blood of bulls and goats to take away sins.