For God having foreordained us unto adoption as sons, made us to be conformed to the body of Christ’s glory.
Having therefore become partakers of Christ, you are properly called Christs [i.e. “anointed ones”]….
Now you have been made Christs, by receiving the…Holy Ghost; and all things have been wrought in you by imitation, because you are images of Christ.
He washed in the river Jordan, and having imparted of the fragrance of His Godhead to the waters, He came up from them; and the Holy Ghost, in the fulness of His being, lighted on Him – like resting upon like.
And to you in like manner, after you had come up from the pool of the sacred streams, there was given an Unction, the anti-type of that wherewith Christ was anointed.
And this is the Holy Ghost; of whom also the blessed Isaiah, in his prophecy respecting Him, said in the person of the Lord, The Spirit of the Lord is upon Me, because He hath anointed Me: He hath sent Me to preach glad tidings to the poor.
For Christ was not anointed by men with oil or material ointment, but the Father having before appointed Him to be the Saviour of the whole world, anointed Him with the Holy Ghost, as Peter says, Jesus of Nazareth, whom God anointed with the Holy Ghost.
David…cried…: Thou hast loved righteousness and hated iniquity; therefore God even Thy God hath anointed Thee with the oil of gladness above Thy fellows.
And as Christ was in reality crucified, and buried, and raised, and you are in Baptism accounted worthy of being crucified, buried, and raised together with Him in a likeness, so is it with the unction also.
As He was anointed with an ideal oil of gladness, that is, with the Holy Ghost, called oil of gladness, because He is the author of spiritual gladness, so you were anointed with ointment, having been made partakers and fellows of Christ.
But beware of supposing this to be plain ointment. For as the Bread of the Eucharist, after the invocation of the Holy Ghost, is mere bread no longer, but the Body of Christ, so also this holy ointment is no more simple ointment…after invocation, but it is Christ’s gift of grace, and, by the advent of the Holy Ghost, is made fit to impart His Divine Nature.
This ointment is symbolically applied to your forehead and your other senses; and while your body is anointed with the visible ointment, your soul is sanctified by the Holy and life-giving Spirit.
Cyril of Jerusalem (c. 313-386): Catechetical Lectures 21, 1-3.