Albert Barnes on Hebrews 10:18

Now where remission of these is. Remission or forgiveness of sins; that is, of the sins mentioned in the previous verse.

There is no more offering for sin. If those sins are wholly blotted out, there is no more need of sacrifice to atone for them, any more than there is need to pay a debt again which has been once paid. The idea of Paul is, that in the Jewish dispensation there was a constant repeating of the remembrance of sins by the sacrifices which were offered, but that in reference to the dispensation under the Messiah sin would be entirely cancelled. There would be one great and all-sufficient sacrifice; and when there was faith in that offering, sin would be absolutely forgiven. If that was the case, there would be no occasion for any further sacrifice for it, and the offering need not be repeated. This circumstance, on which the apostle insists so much, made a very important difference between the new covenant and the old. In the one, sacrifices were offered every day; in the other, the sacrifice once made was final and complete: in the one case, there was no such forgiveness, but that the offender was constantly reminded of his sins by the necessity of the repetition of sacrifice; in the other, the pardon was so complete that all dread of wrath was taken away, and the sinner might look up to God as calmly and joyfully as if he had never been guilty of transgression.