John Chrysostom

"Nor yet that He should offer Himself often, as the High Priest entereth into the Holy place every year with blood of others." Seest Thou how many are the differences? The "often" for the "once"; "the blood of others," for "His own." Great is the distance. He is Himself then both victim and Priest and sacrifice. For if it had not been so, and it had been necessary to offer many sacrifices, He must have been many times crucified. "For then," he says, "He must often have suffered since the foundation of the world."

Homily on Hebrews 17 ↗

Theophylact of Ohrid

But He did not enter heaven now in order to enter again a second time, offering Himself. Notice the superiority of Christ. The former — "every year," Christ — once. And in this is the superiority. That one — "with the blood of others," of calves and goats, but Christ — with His own.

Commentary on Hebrews ↗

Oecumenius

"now to appear." With the flesh, he says, it appears. "in the presence of God." What do you say? Unless he had entered into heaven, he would not appear in the sight of the Father, who is present everywhere and fills all things? Do you see that these are humble matters of privilege? "on our behalf." When the victim of his own body ascended to appear before the Father for us, this is to reconcile us to himself. Indeed, having made mention of the flesh, blessed Paul speaks boldly of all things humble. …

The Pseudo-Oecumenian Catena on Hebrews ↗

Thomas Aquinas

468. – Then (v. 25) he shows that the cleansing effected by the New Testament is more complete than that of the Old. But he shows this in two ways: first, by the fact that the former were repeated every day, but this only once. Likewise, as to its effects, because the former could not remove sin, but this one can. In regard to this he does two things: first, he describes the first; secondly, the second (chap. 10). …

Commentary on Hebrews ↗