BROTHERS and SISTERS, when Christ appeared as the High Priest of the blessings to come, He entered through the greater and more perfect tabernacle, one not made with hands, that is, one not of this present creation. And not through the blood of goats and calves, but through His own Blood, He entered into the Holy Place once for all, thus obtaining eternal redemption. For if the blood of goats and bulls, and the ashes of a heifer, through the sprinkling of those who have been defiled, sanctifies them, so that their flesh is purified, how much more will the Blood of Christ, Who through the Holy Spirit offered Himself blamelessly to God, purify our conscience from dead works to worship the living God?
Saint Theodoret of Cyrus explains why we still celebrate the Liturgy, even though our High Priest, the Lord Jesus, has "entered into the Holy Place once for all, thus obtaining eternal redemption":
If the priesthood established by the Law has come to an end, and the Priest, Who is "in the order of Melchizedek" has offered His sacrifice, and has made all other sacrifices unnecessary, why do the priests of the New Covenant perform the mystical Liturgy? Now it is clear to those instructed in divinity that we do not offer another sacrifice, but perform a memorial of that unique and saving offering. For this was the Lord's own command, "Do his in remembrance of Me" (1 Corinthians 11:24). So that by contemplation we may recall what is symbolized, the sufferings endured on our behalf, and may kindle our love towards our benefactor, and look forward to the enjoyment of the blessings to come.