Who are the "brothers" in this psalm? Is it just about family?
The psalm never says, so the commentators answer differently. The Gemara says Moshe and Aharon, who were brothers. Rashi says the brothers are the Jewish people, whom the Tanach calls brothers and friends, and that the "also" in "also together" is God, living among them in the Temple.
Radak says it is about the future king Messiah and the High Priest. Both are leaders, and they will be brothers in greatness who are not jealous of each other.
Metzudat David (a commentary from the 1700s) reads it as all of Israel living on its land under one kingdom, never split into two again.
The Malbim (Rabbi Meir Leibush, a Bible commentator in Eastern Europe, who died in 1879) says the brothers are the tribes Yissachar and Zevulun. Zevulun traded and earned, so Yissachar could learn Torah. Together they had the lasting good and the pleasant things of this world.
Sefer Chasidim applies the verse to brothers, to fathers and sons, and to teachers and students, and adds a warning: when they keep fighting, it is better that they not be together.
These are separate explanations. Rashi mentions the Gemara's reading and still says the main meaning is the Temple. The others simply give their own reading.
Horayot 12a,Rashi on Tehillim 133:1 and 133:2,Radak on Tehillim 133:1,Metzudat David on Tehillim 133:1,Malbim on Tehillim 133:1 and 133:3,Sefer Chasidim 343Why does a poem about getting along talk about oil on a beard?
The psalm gives two pictures. Fine oil on the head runs down onto the beard and then to the collar. Dew from Hermon falls on Zion. Rashi says the oil is the anointing oil used on Aharon the priest. Just as that oil stands for greatness, he says, Mount Zion stands for glory and honor for Israel.
Metzudat David says the point is that the oil does not stay put. It spills from the head onto the beard and the collar. In the same way, when the people are united under one head, the king, the blessing reaches everyone through him.
Meiri reads the oil as the priesthood. Oil floats above every other liquid and is smooth, he says, which points to humility. He thinks the detail of it running down to someone else shows the last stage of wisdom: giving to others. The dew, for him, is the king. Everyone needs dew every day, so a king should rule steadily, not like a flood.
The Malbim adds that the oil was meant for the head, yet it overflowed onto the beard. Blessing can come in such plenty that it also reaches people who were not ready for it.
Metzudat David, Meiri and the Malbim read the picture differently, but in all three, what comes down does not stop with the first one who receives it.
Rashi on Tehillim 133:2,Metzudat David on Tehillim 133:2,Meiri on Tehillim 133:2 to 133:3,Malbim on Tehillim 133:2What does a psalm about a priest's oil have to do with Chanukah?
As with Tehillim 33 just before it, we found no source that says why this psalm is printed after the lights. But oil ties the psalm to Chanukah, and two Chassidic writers say so.
The psalm's oil, Rashi says, is the anointing oil used on Aharon the priest.
Chanukah is about oil and priests too. The Gemara says the Greeks made all the oil in the Temple impure. When the Hasmoneans (the family of Matityahu, who led the revolt) won, they found one jar still sealed with the seal of the High Priest, enough for one day. The Rambam (Maimonides, who died in 1204) writes that the Hasmoneans were High Priests.
The Bnei Yissaschar, by Rabbi Tzvi Elimelech of Dinov (a Chassidic rebbe in Galicia, in the 1800s, whose prayer opens this lighting service in the siddur), says the psalm hints at Chanukah. "Like the good oil" is what happened in the Chanukah miracle: with good oil came light. The first spark on this prayer shows how he gets there.
Rabbi Natan of Breslov (the main student of Rabbi Nachman, a Chassidic teacher who died in 1810) writes in Likutei Halakhot that the oil of the Chanukah light is like the holy anointing oil, and he quotes this verse. For him that oil stands for the light of knowledge, which should grow every day, the way the Chanukah lights grow each night.
Neither one says this is why the psalm is printed here. Another Gemara is about the anointing oil Moshe made in the desert. It was only twelve log (a measure of liquid), yet it anointed the Tabernacle, its vessels, Aharon and his sons for seven days, and then High Priests and kings after them. The Gemara says many miracles were done with it, and that all of it will still be there in the future.
So the jar and the anointing oil are both a small amount of holy oil that lasted far longer than it should. That comparison is ours. No source we found makes it.
Rashi on Tehillim 133:2,Shabbat 21b,Rambam, Laws of Megillah and Chanukah 3:1,Keritot 5b,Bnei Yissaschar, Kislev and Tevet 2:44,Likutei Halakhot, Choshen Mishpat, Laws of Paid Guardians 2:2,Siddur Sefard, Chanukah, Menorah Lighting 4