Then Samuel took a vial of oil, and poured it upon his head, and kissed him, and said, Is it not because the LORD has anointed you to be ruler over his inheritance?
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George Leo Haydock
Vial, in the form of a lentil. (Pliny, xviii. 12.)
Oil. This anointing seems to have been peculiar to the kings, priests, and prophets of the Hebrews, who prefigured Jesus, the great anointed of God. (St. Augustine in Psalm xliv.) The custom was very ancient, Judges ix. 8. It is thought that those kings, who succeeded their fathers by their birth-right, and without opposition, did not receive any unction. (Calmet)
But the silence of Scripture is no proof on this head; and the Fathers seem to be convinced that the custom subsisted till Christ appeared. (St. Justin Martyr, Dialogue with Trypho, etc.) (Haydock)
The Rabbins pretend that the sacred ointment was used for the kings of Juda, but not for those of Israel. It is not probable that it was used for either, Exodus xxx. 32., and 3 Kings i. 39. We read that Jehu was anointed king of Israel; (4 Kings ix. 6,) and we may suppose that common oil was used, in his regard, as well as for the other kings. The perfume or balm of Judea, does ...
And of all people, we Christians alone are those who … celebrate the mystery and are anointed there with the unspeakable chrism from a horn, as David (was anointed), not from an earthen vessel, he says, as (was) Saul, who held converse with the evil demon of carnal concupiscence. - "The Refutation of All Heresies 5.4" ...
Furthermore, whenever someone had to be chosen and anointed, the grace of the Spirit would wing its way down and the oil would run on the forehead of the elect. Prophets fulfilled these ministries. - "Discourses Against Judaizing Christians 6.4.3"