When you were baptized into Christ and clothed yourselves in him, you were transformed into the likeness of the Son of God.
Having destined us to be his children by adoption, God gave us a likeness to Christ in his glory, and, living as you do in communion with Christ, you yourselves are rightly called ‘christs’ or anointed ones.
When he said: Do not touch my anointed ones, God was speaking of you.
You became ‘christs’ when you received the sign of the Holy Spirit.
Indeed, everything took place in you by means of images, because you yourselves are images of Christ.
Christ bathed in the river Jordan, imparting to its waters the fragrance of his divinity, and when he came up from them the Holy Spirit descended upon him; like resting upon like.
So you also, after coming up from the sacred waters of Baptism, were anointed with chrism, which signifies the Holy Spirit, by whom Christ was anointed and of whom blessed Isaiah prophesied in the name of the Lord:
The Spirit of the Lord is upon me, because he has anointed me; he has sent me to preach good news to the poor.
Christ’s anointing was not by human hands, nor was it with ordinary oil. On the contrary, having destined him to be the Saviour of the whole world, the Father himself anointed him with the Holy Spirit.
The words of Peter bear witness to this: Jesus of Nazareth, whom God anointed with the Holy Spirit.
And David the prophet proclaimed: Your throne, O God, shall endure forever, your royal sceptre is a sceptre of justice. You have loved righteousness and hated iniquity; therefore God, your God, has anointed you with the oil of gladness above all your fellows.
The oil of gladness with which Christ was anointed was a spiritual oil; it was in fact the Holy Spirit himself who is called the oil of gladness because he is the source of spiritual joy.
But you also have been anointed with oil, and by this anointing you have entered into fellowship with Christ and have received a share in his life.
Beware of thinking of this chrism as merely ordinary oil. As the eucharistic bread after the invocation of the Holy Spirit is no longer ordinary bread but the body of Christ, so also the oil after the invocation is no longer plain ordinary oil but Christ’s gift which by the presence of his divinity becomes the instrument through which you receive the Holy Spirit.
While symbolically, on your foreheads and organs of sense, your bodies are anointed with this oil that we see; your souls are sanctified by the holy and life-giving Spirit.
Cyril of Jerusalem (c. 313-386): Catechesis 21, 1-3 (PG 33:1087-1091); from the Monastic Office of Vigils, Easter Wednesday, Year 2.