Why couldn't animal sacrifices in the Old Testament actually atone for sin?
In the Old Testament economy, the atoning blood of Christ had not yet been shed, so animal blood could not atone for anyone's sin. Those sacrifices did not atone; they merely covered sin. Because true atonement was not yet accomplished, the Old Testament believer could not go up into God's presence, but went down into paradise.
Les explains that in the Old Testament economy, since the atoning blood of Christ had not yet been shed, animal blood could not atone for anyone's sin; all the sacrifices did was cover it. Because the Old Testament believer could not go up into the presence of God, he went down into paradise. Les then connects this to Matthew 12:38-40 and the sign of Jonah: as Jonah was three days and three nights in the whale's belly, so the Son of man would be three days and three nights in the heart of the earth. Everything concerning paradise in the Old Testament economy until after Christ's resurrection was down in the center of the earth.