Adam Clarke on Hebrews 9:12

But by his own blood - Here the redemption of man is attributed to the blood of Christ; and this blood is stated to be shed in a sacrificial way, precisely as the blood of bulls, goats and calves was shed under the law.

Once - Once for all, εφαπαξ, in opposition to the annual entering of the high priest into the holiest, with the blood of the annual victim.

The holy place - Or sanctuary, τα ἁγιᾳ, signifies heaven, into which Jesus entered with his own blood, as the high priest entered into the holy of holies with the blood of the victims which he had sacrificed.

Eternal redemption - Αιωνιαν λυτρωσιν· A redemption price which should stand good for ever, when once offered; and an endless redemption from sin, in reference to the pardon of which, and reconciliation to God, there needs no other sacrifice: it is eternal in its merit and efficacy.