The Oily BoidBy Rabbi Jack Abramowitz
A Song of Ascents by David: Behold, how good and pleasant it is when brothers dwell together in unity! Who are these “brothers?” Different interpretations include the Jewish people as a whole, Moses and Aaron, or the Moshiach (the messiah) and the Kohein Gadol (High Priest) that will serve in his day. In any case, this unity is a very good thing. It is compared to two other excellent things:
1) The precious oil used to anoint Aaron as the first High Priest, which rolled down his head into his beard.
2) The dew of Chermon, a high mountain in Jerusalem, which would roll down onto other, lower mountains.
It was from these mountains that G-d commanded a blessing of eternal life (that is, in the Next World).
According to the opinion that the “brothers” are the Moshiach and the Kohein Gadol, the oil is a metaphor for the latter and the dew is a metaphor for the former.
This Psalm in its entirety (three verses!) is used by the Talmud (Horayos 12a) in a discussion relating to the possibility of misuse of the anointing oil.