Entering the Biblical Book of Prayer 2 - Psalms 24 and 114

...Two priests stand at the marble table of the fats, where the limbs and fats were placed before being taken to the altar, and there were two silver trumpets in their hands. These two priests sounded a tekia, a long continuous blast; they then sounded a terua, a series of staccato blasts; and lastly they sounded another tekia to alert the Levites to prepare to recite the psalm. The priests with the trumpets came and stood near ben Arza, the title given to the person who was tasked with striking the cymbals, one to his right and one to his left. Then the High Priest stooped to pour the libation, and the Deputy waved the cloths, and ben Arza struck the cymbals, and the Levites recited the psalm of that day of the week.

Each psalm was divided into three sections. Whenever the Levites reached the end of one section of the psalm, the priests sounded a tekia, and the people in the courtyard prostrated themselves. At the end of each section there was a tekia, and for every tekia there was a prostration. ...

Tractate Soferim (Scribes) is a rabbinic discussion of laws related to writing and reading of holy scrolls, among other matters. It was likely compiled in the 8th century in the land of Israel.

...the people have adopted the custom of saying psalms at their proper times; as we have learned in the Mishnah: ‘These were the psalms which the Levites used to recite in the Temple: On Sunday they used to recite, The earth is the Lord’s, and the fulness thereof; the world, and they that dwell therein. ...

For whoever makes mention of a Biblical verse at its proper time is regarded [by God] as though he had built a new altar and offered a sacrifice upon it.

(1) Of David. A psalm.

The earth is the LORD’s and all that it holds,
the world and its inhabitants. (2) For He founded it upon the ocean,
set it on the nether-streams.

(3) Who may ascend the mountain of the LORD?
Who may stand in His holy place?— (4) He who has clean hands and a pure heart,
who has not taken a false oath by My life
or sworn deceitfully. (5) He shall carry away a blessing from the LORD,
a just reward from God, his deliverer. (6) Such is the circle of those who turn to Him,
Jacob, who seek Your presence. Selah.

(7) O gates, lift up your heads!
Up high, you everlasting doors,
so the King of glory may come in! (8) Who is the King of glory?—
the LORD, mighty and valiant,
the LORD, valiant in battle. (9) O gates, lift up your heads!
Lift them up, you everlasting doors,
so the King of glory may come in! (10) Who is the King of glory?—
the LORD of hosts,
He is the King of glory! Selah.

(1) The LORD is king,
He is robed in grandeur;
the LORD is robed,
He is girded with strength.
The world stands firm;
it cannot be shaken. (2) Your throne stands firm from of old;
from eternity You have existed. (3) The ocean sounds, O LORD,
the ocean sounds its thunder,
the ocean sounds its pounding. (4) Above the thunder of the mighty waters,
more majestic than the breakers of the sea
is the LORD, majestic on high. (5) Your decrees are indeed enduring;
holiness befits Your house,
O LORD, for all times.

Eighteen days and one night (in the year) the Hallel is recited. These are: the eight days of Sukkot, the eight days of Hanukkah, the first festival day of Passover and its night, and the festival of Shavuot.

The Gemara asks: And since there is the great hallel, [DR: 'Great Hallel' is a rabbinic name for Psalm 136] which contains the special praise of “Who gives food to all flesh” (Psalms 136:25), as explained above, what is the reason that one also recites this hallel of Psalms 113–118, the section recited on every joyous occasion?

The Gemara answers: The reason is because the regular hallel contains these five matters: The remembrance of the exodus from Egypt, the splitting of the Red Sea, the giving of the Torah, the resurrection of the dead, and the pangs of the Messiah. Since it mentions these key concepts, this hallel is also considered important.

(1) When Israel went forth from Egypt,
the house of Jacob from a people of strange speech, (2) Judah became His holy one [NJPS note: or 'sanctuary'],
Israel, His dominion. (3) The sea saw them and fled,
Jordan ran backward, (4) mountains skipped like rams,
hills like sheep. (5) What alarmed you, O sea, that you fled,
Jordan, that you ran backward, (6) mountains, that you skipped like rams,
hills, like sheep? (7) Tremble, O earth, at the presence of the Lord [אדון / Adon / Lord],
at the presence of the God of Jacob, (8) who turned the rock into a pool of water,
the flinty rock into a fountain.

The Gemara elaborates: The exodus from Egypt, as it is written: “When Israel came forth out of Egypt, the house of Jacob from a people of strange language” (Psalms 114:1). And the splitting of the Red Sea, as it is written: “The sea saw it and fled; the Jordan turned backward” (Psalms 114:3). The giving of the Torah, as it is written: “The mountains skipped like rams” (Psalms 114:4), which is similar to the description of the giving of the Torah found elsewhere in the books of the Prophets. The resurrection of the dead, as it is written: “I will walk before the Lord in the lands of the living” (Psalms 116:9), which follows the verse: “For you have delivered my soul from death.” After mentioning death, the psalm describes the resurrection in the lands of the living.

(49) ה' will bring a nation against you from afar, from the end of the earth, which will swoop down like the eagle—a nation whose language you do not understand,

Commentary by Rabbi David Kimchi, Radak (1160–1236) of Provence.

Mountains [skipped like rams, hills like sheep] - 'Mountains' in the plural. It is possible that other mountains close to Mount Sinai trembled and quaked [in response to the revelation of the Ten Commandments].