What should the Old Testament word atonement really have meant?
The Old Testament term atonement should really have meant covering, a sweeping of sins under the rug. It was a misnomer, because the high priest's sacrifices never took away a single sin; they were only a stopgap until Christ's blood was shed and true atonement finalized.
Les explains that atonement is one of those doctrinally heavy words, like justification and eternal life. As it is used in the Old Testament, however, it was not the appropriate word for the Day of Atonement. Even though the high priest did everything exactly right and offered the blood of the sacrifice on the Holy of Holies and on the mercy seat, it never took away a single sin. It was simply a stopgap waiting for the coming of Christ. So the word atonement was a misnomer. It should have been a word that had to do with covering, or as he often says, a sweeping under the rug. That is actually what God was doing with the sins of the Old Testament believer: He swept them under the rug until the true atonement was finalized when the blood of Christ was shed. Then all that stuff under the rug was atoned for, taken away, and forgiven.