Wherefore, whatever is offered to God in order to
raise man's spirit to Him, may be called a sacrifice.

Now man is required to offer sacrifice for three reasons. First, for
the remission of sin, by which he is turned away from God. Hence the
Apostle says (Heb. 5:1) that it appertains to the priest "to offer
gifts and sacrifices for sins." Secondly, that man may be preserved
in a state of grace, by ever adhering to God, wherein his peace and
salvation consist. Wherefore under the old Law the sacrifice of
peace-offerings was offered up for the salvation of the offerers, as
is prescribed in the third chapter of Leviticus. Thirdly, in order
that the spirit of man be perfectly united to God: which will be most
perfectly realized in glory. Hence, under the Old Law, the holocaust
was offered, so called because the victim was wholly burnt, as we
read in the first chapter of Leviticus.

Now these effects were conferred on us by the humanity of Christ.
For, in the first place, our sins were blotted out, according to Rom.
4:25: "Who was delivered up for our sins." Secondly, through Him we
received the grace of salvation, according to Heb. 5:9: "He became to
all that obey Him the cause of eternal salvation." Thirdly, through
Him we have acquired the perfection of glory, according to Heb.
10:19: "We have [Vulg.: 'Having'] a confidence in the entering into
the Holies" (i.e. the heavenly glory) "through His Blood." Therefore
Christ Himself, as man, was not only priest, but also a perfect
victim, being at the same time victim for sin, victim for a
peace-offering, and a holocaust.

Reply Obj. 1: Christ did not slay Himself, but of His own free-will
He exposed Himself to death, according to Isa. 53:7: "He was offered
because it was His own will." Thus He is said to have offered Himself.

Reply Obj. 2: The slaying of the Man Christ may be referred to a
twofold will. First, to the will of those who slew Him: and in this
respect He was not a victim: for the slayers of Christ are not
accounted as offering a sacrifice to God, but as guilty of a great
crime: a similitude of which was borne by the wicked sacrifices of
the Gentiles, in which they offered up men to idols. Secondly, the
slaying of Christ may be considered in reference to the will of the
Sufferer, Who freely offered Himself to suffering. In this respect He
is a victim, and in this He differs from the sacrifices of the
Gentiles.

(The reply to the third objection is wanting