The only spotless priest without sin

The Proper Mass of the Feast of Reparation for Offenses Committed Against the Most Holy Sacrament (Thursday after Sexagesima) contains the following beautiful Preface:

It is very meet and right,
just and availing unto salvation,
that always and everywhere we should give thanks unto Thee,
O Lord, holy Father, almighty, everlasting God,
through Jesus Christ our Lord:
Who is the true and eternal Pontiff,
the only spotless priest without sin,
by whose Blood the hearts of the faithful are cleansed:
Whom, by His own institution, we do immolate
not only through offerings for the sins of the people,
but also for our own offenses.
Through Whom the Angels praise,
the Dominations adore,
the Powers fear Thy majesty.
The Heavens and the Heavenly Virtues
and the blessed Seraphim
together sing Thy praise with exultation.
With whom, we beseech Thee,
Bid that our voices also be admitted,
humbly praising Thee, and saying:
Holy, Holy Holy.