After this, when we have issued from the font, we are thoroughly anointed with a blessed unction,—(a practice derived) from the old discipline, wherein on entering the priesthood, men were wont to be anointed with oil from a horn, ever since Aaron was anointed by Moses. Whence Aaron is called “Christ,” from the “chrism,” which is “the unction;” which, when made spiritual, furnished an appropriate name to the Lord, because He was “anointed” with the Spirit by God the Father; as written in the Acts: “For truly they were gathered together in this city against Thy Holy Son whom Thou hast anointed.” Thus, too, in our case, the unction runs carnally, (i.e. on the body,) but profits spiritually; in the same way as the act of baptism itself too is carnal, in that we are plunged in water, but the effect spiritual, in that we are freed from sins.
Reproduced in full. Translation: Ante-Nicene Fathers, vol. 3 (Roberts and Donaldson, 1885), public domain (Public domain).