Midrash su Salmi 81:2

Another matter: “Your hair is like a flock of goats that streams down [shegaleshu] from Mount Gilad” (Song of Songs 4:1) – the mountain from whose midst you took away [shegelashten], I rendered a memorial for the nations of the world. Which is this? These are the priestly watches. What is it that you took away from its midst? “Your teeth are like a flock of ordered ewes” (Song of Songs 4:2) – defined matters, the twenty-four priestly watches, the twenty-four Levite watches, and twelve divisions.⁵⁴These were divisions of men who would come for a month at a time to perform whatever labors the king would assign them (Etz Yosef). “That have come up from bathing” (Song of Songs 4:2) – who protect Israel. “That are all paired” – as we learned there: At three times during the year all the priestly watches were equal (Sukka 55b). “And there is none missing among them” (Song of Songs 4:2) – as we learned: “The first, the head and the hind leg…” (Tamid 31a).⁵⁵Each of the priests had a role, and there were always enough priests to perform each task.
“Your lips are like a scarlet thread” (Song of Songs 4:2) – as we learned: [The High Priest] stooped to pour the libation, and the deputy waved the cloths, and ben Arza struck the cymbals (Tamid 33b).⁵⁶This was the sign for the Levites to begin their song in the Temple. “Your speech is lovely” (Song of Songs 4:2) – this is the song, as we learned there: The song that the Levites would recite in the Temple. On the first day they would recite: “The earth is the Lord’s and all it contains” (Psalms 24:1).⁵⁷The intention is that on Sunday the Levites would recite the entire chapter of Psalms beginning with this verse. The same is true for all of the citations cited here; one psalm was recited each day of the week. On the second day: “Great is the Lord and highly to be praised in the city of God…” (Psalms 48:2). On the third day: “God stands in the divine congregation” (Psalms 82:1). On the fourth day: “Lord God, to whom vengeance belongs, God to whom vengeance belongs, shine forth” (Psalms 94:1). On the fifth day: “Sing for joy to God, our strength; shout aloud to the God of Jacob” (Psalms 81:2). On the sixth day: “The Lord reigns: He is robed in majesty” (Psalms 93:1). On Shabbat they would recite: “A psalm, a song for the Shabbat day” (Psalms 92:1) – for the future, for the day that will be entirely Shabbat and rest for everlasting life.

... Another explanation. Why does the verse (Psalms 81:2) mention Yaakov and not all of the forefathers? Our rabbis taught: a man is measured with the measure by which he measures, as it says “In that measure (b’saseah), when they sent them out, it strove with it…” (Isaiah 27:8) A seah with a seah. I only know seah, from where do I learn tirkav and a half tirkav, kab and a half kav, rovah and a half rovah, a tuman and an uchlah? Scripture says “For every victory shout (s’on soein) sounds with clamor…” (Isaiah 9:4) Here there are many measures. I only know about something which comes by measure, from where do I learn little bits that add up to a large amount? Scripture says “…adding one to another to find out the account.” (Ecclesiastes 7:27) This is like a king who had three people that loved him, and sought to build himself a palace. He brought the first one and said to him: I want to build a palace for myself. His love replied to him: I recall that it was a mountain in the beginning. He called to the second love and said to him: I want to build a palace for myself. He replied: I recall that it was a field in the beginning. He called to the third love and said: I want to build a palace for myself. He replied: I recall that it was a palace in the beginning. He said to him: by your life! I will build that palace and call it by your name. So too Avraham, Yitzchak and Yaakov were lovers of the Holy One. Avraham called the Holy Temple ‘mountain,’ as it says “On the mountain, the Lord will be seen.” (Genesis 22:14) Yitzchak called it field, as it says “…the fragrance of my son is like the fragrance of a field…” (Genesis 27:27) Yaakov called it ‘house’ even before it was built, as it says “This is none other than the house of God…” (Genesis 28:17) The Holy One said to him: by your life! You called it a house before it was built and I will call it by your name, as it says “Come, let us go up to the Lord's mount, to the house of the God of Jacob…” (Isaiah 2:3) So too Jeremiah said “So said the Lord: Behold I am returning the captivity of the tents of Jacob…” (Jeremiah 30:18) So too Asaf decorated his words and only recalled the God of Yaakov with a trumpet blast, as it says “…sound the shofar to the God of Jacob.” (Psalms 81:2)