The writer points to something his readers could see for themselves: the sacrifices kept being offered, year after year. If they had truly taken sin away, why repeat them? Barnes uses a picture from medicine: "If what is given to a patient heals him, there is no need of repeating it; but if it is repeated often it shows that there was some deficiency in it." The second half of the sentence gives the reason: once truly cleansed, the worshippers "should have had no more conscience of sins." Barnes explains that phrase as having "no more trouble of conscience on account of them."

The writer answers at once. Instead of ending sin, "in those sacrifices there is a remembrance again made of sins every year" (Hebrews 10:3), because "it is not possible that the blood of bulls and of goats should take away sins" (Hebrews 10:4). Then he shows what does: "we are sanctified through the offering of the body of Jesus Christ once for all" (Hebrews 10:10). Christ "offered one sacrifice for sins for ever" and "sat down on the right hand of God" (Hebrews 10:12). The conclusion: "there is no more offering for sin" (Hebrews 10:18).

Once a year, on the Day of Atonement, the high priest entered the most holy place "not without blood" (Hebrews 9:7) to make "an atonement for the children of Israel for all their sins once a year" (Leviticus 16:34). The Greek word for "conscience" here is suneidesis, consciousness or conscience. "Once" is hapax, once or once for all, and "purged" is katharizo, to cleanse. Gill explains that for those once purged by the blood of Christ, "no more conscience of sins" means "not that they have no sin, or no sense of sin," but "that they are discharged from the guilt of sin, and are not liable to condemnation for it."

This question shows that God's plan was always to deal with sin completely. The yearly sacrifices were a shadow, not the reality (Hebrews 10:1). Their very repetition announced that something more was needed. That something was the willing offering of Christ: "Lo, I come to do thy will, O God" (Hebrews 10:9).

The result is a people of whom God says, "their sins and iniquities will I remember no more" (Hebrews 10:17). Barnes is careful here: "The pardon of sin does not cause it to cease to be remembered" by the forgiven person. But the memory no longer crushes. In his words, "it will no longer overwhelm the mind with the dread of hell."