John Chrysostom

"Neither by the blood," he says, "of goats and calves" (All things are changed) "but by His own Blood" (he says) "He entered in once for all into the Holy Place." See thus he called Heaven. "Once for all" (he says) "He entered into the Holy Place, having obtained eternal redemption." And this [expression] "having obtained," was [expressive] of things very difficult, and that are beyond expectation, how by one entering in, He "obtained everlasting redemption."

Homily on Hebrews 15 ↗

Theophylact of Ohrid

Behold, everything has changed, and to the same degree as the Blood of the Lord surpasses the blood of animals with which the high priest of the law entered. That is, to heaven. Not a temporary purification, like those, but an eternal liberation of souls from sins. Or, that having entered once, through one entrance He accomplished for us an eternal benefit. …

Commentary on Hebrews ↗

Thomas Aquinas

439. – Thirdly, he shows how he entered, because not without blood; but he with the blood of calves and goats, as it says in Leviticus (chap. 16); but Christ not so, i.e., not with another's blood: taking not the blood of goats or of calves but his own blood, which He offered on the cross for our salvation: 'This is my blood of the New Testament, which shall be shed for you and for many unto the remission of sins' (Mt. 26:28). …

Commentary on Hebrews ↗