The oil of gladness

AS He was anointed with an ideal (νοητῷ) oil of gladness, that is, with the Holy Ghost, called oil of gladness, because He is the author of spiritual (πνευματίκῆς) gladness, so ye 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, nor (so to say) common, 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

Which ointment is symbolically applied to thy forehead and thy other senses; and while thy body is anointed with the visible ointment, thy soul is sanctified by the Holy and life-giving Spirit.

St Cyril of Jerusalem (?315-386). Catechetical Lecture XXI. On The Mysteries III (Holy Chrism), §2-3.

IN mercy, O Good One, look with thine eye upon this our prayer, we who are gathered together in thy holy temple this day, to make chrism with holy oil upon thine ailing servants.

Exaposteilarion in the Order of Holy Unction.