Theophylact of Ohrid

If forgiveness of sins was granted through a single sacrifice, then what need is there after this for a second sacrifice? Therefore it is indicated that we, having received the forgiveness of sins, were brought to perfection by the single offering of Christ, and no longer have need of another sacrifice. Thus, the Jewish sacrifices are unnecessary and, being performed out of stubbornness, have long been recognized as useless by those who now perform them.

Commentary on Hebrews ↗

Oecumenius

"Now where there is forgiveness of these things." Of sins, obviously. "there is no longer an offering for sin." For who, he says, has need of many offerings, when the one that Christ presented is sufficient to take away sins?

The Pseudo-Oecumenian Catena on Hebrews ↗

Thomas Aquinas

He forms the following reason: Sins are remitted in the New Testament by Christ's sacrifice, because the blood of Christ was shed for the remission of sins; therefore, in the New Testament, in which sins and iniquities are forgiven, as the authority indicates, there is no offering to be repeated for sins: 'They that are in health need not a physician, but they that are ill' (Mt. 9:12). Therefore, where there is forgiveness of sins, there is no longer any offering for sin. For this would be to demean Christ's sacrifice.

Commentary on Hebrews ↗