Thomas Aquinas

“ Nevertheless since Extreme Unction confers grace and remission of sins, there is no doubt that it possesses an enlightening and cleansing power, even as Baptism, though not so copious.
Art. 2 - Whether Extreme Unction is one sacrament? Objection 1: It would seem that Extreme Unction is not one sacrament. Because the oneness of a thing depends on its matter and form, since being and oneness are derived from the same source. Now the form of this sacrament is said several times during the one administration, and the matter is applied to the person anointed in respect of various parts of his body. ”

“ Although, in the Eucharist, if the priest die after the consecration of the bread, another priest can go on with the consecration of the wine, beginning where the other left off, or can begin over again with fresh matter, in Extreme Unction he cannot begin over again, but should always go on, because to anoint the same part a second time would produce as much effect as if one were to consecrate a host a second time, which ought by no means to be done. ”

“ Because the consecration of the Eucharistic elements surpasses that of the matter in this sacrament. But a priest can consecrate the matter in the Eucharist. Therefore he can do so in this sacrament also.
Objection 2: Further, in material works the higher art never prepares the matter for the lower, because the art which applies the matter is more excellent than that which prepares it, as stated in Phys. ii, text. 25. Now a bishop is above a priest. Therefore he does not prepare the matter of a sacrament which is applied by a priest. ”

“ But He did not use this sacrament, nor any bodily anointing, wherefore in all anointings a consecrated matter is required. The second reason is that this sacrament confers a plenitude of grace, so as to take away not only sin but also the remnants of sin, and bodily sickness. The third reason is that its effect on the body, viz. bodily health, is not caused by a natural property of the matter. wherefore it has to derive this efficacy from being consecrated. ”

“ First, as something indivisible, which is neither actually nor potentially several---as a point, and unity. Secondly, as something continuous, which is actually one, but potentially several---as a line. Thirdly, as something complete, that is composed of several parts---as a house, which is, in a way, several things, even actually, although those several things go together towards making one. ”