After repeating several earlier observations about the insufficiency of the Levitical priesthood and the powerlessness of the Old Testament sacrifices according to their essence, the Apostle dwells chiefly on Old Testament prophecies concerning the abolition of the Old Testament sacrifices and priesthood.
“For the law, having a shadow of the good things to come, and not the very image of the realities, can never by the same sacrifices year by year,” that is, on the Day of Atonement, “which they offer continually, make perfect those who approach.”
That means it can never make them perfect, or grant inward cleansing.
“Otherwise, would they not have ceased to be offered, since the worshipers, once cleansed, would have had no more consciousness of sins?” (Heb 10:1-2).
The Apostle’s thought is this. If the sacrifice of atonement offered by the Israelite high priest had power to produce perfect cleansing, as the sacrifice of Jesus Christ does, then its offering would have ceased.
Those who offered it and those for whom it was offered, once cleansed, would have ceased, like Christians, to be conscious of their sinful guilt.
Granted, Christians at the present time also know themselves to be sinful people. They are carried away by the force of sinful desires, which continue to live in them even after gracious regeneration. They too can fall, and do fall, into various sins.
Yet this in no way troubles them to the degree that there would be need again for the repetition of Christ’s bloody sacrifice for their sins.
On the contrary, they know and feel in their souls that by the death of Jesus Christ their responsibility and punishment for sins have been removed once for all.
In general, for those who appropriate the merits of Christ the Savior through active faith in Him, sin as it were ceases to exist, and therefore is driven from their consciousness.