Midrash su Salmi 119:164

You find that not all the eighteen benedictions (of the Amidah) recited each day are in praise of the Holy One, blessed be He. In fact, only the first three and the final three are in praise of Him, while the twelve intervening prayers allude to human needs. It is for this reason that we do not say the eighteen benedictions on the Sabbath.³On Sabbaths and holy dayss the thirteen intervening blessings are omitted lest the holiness of the day be marred by references to mundane affairs; a single benediction describing the characteristic feature of the day is inserted, in their place. For, if it should happen that a loved one was ill at home at the time of praying, the worshipper would be reminded of it while reciting the prayer “Who healeth the ills of His people” and would become depressed. Inasmuch as the Sabbath was given to Israel for sanctification, for joy and rest and not for sorrow, one must recite the first three blessings and the final three blessings (of the Amidah) and replace the intervening ones with the prayer of Rest. Hence, David proclaimed: Seven times a day do I praise Thee, because of Thy righteous ordinances (Ps. 119:164). The word seven in this verse refers to the seven benedictions recited on the Sabbath. What other day could this verse refer to, if not the day of rest, which is unlike any other? For it is said: Remember the Sabbath day and keep it holy (Exod. 20:8)—in every respect, even from in the pursuit of thy business and speaking thereof (Isa. 58:13).

(Numb. 8:5-6:) “Then the Lord spoke [unto Moses saying], ‘Take the Levites.’” Let our master instruct us: How many strings were on the harp which the Levites played?¹Numb. R. 15:11. So said R. Judah:²T‘Arakh. 2:7; ‘Arakh. 13b. There were seven (shb') strings on that harp, as stated (in Ps. 16:11), “In Your presence there is fullness (rt.: sb')³Since the S here is a Hebrew sin in the unpointed text SB‘ is identical with ShB‘. of joy.” Do not read [the word pointed as] sova' ("fullness") but [as] sheva' ("seven"). So also did David say (in Ps. 119:164), “With seven a day do I praise You.⁴M. Pss. 81:3; PR 21:1. A more traditional translation of Ps. 119:164 would read: SEVEN TIMES A DAY DO I PRAISE YOU. Moreover, in the days of the messiah it will be made with eight [strings]. Therefore David has stated concerning the instrumental music (in Ps. 6:1), “For the leader; with instrumental music on the eight-stringed harp.” Furthermore in the future it will be made of ten [strings] as stated (in Ps. 144:9), “O God, let me sing to You a new song; let me play for You on a ten-stringed harp.” And who ordained them? Samuel and David, as stated (in I Chron. 9:22), “David and Samuel the seer ordained them in their office of trust.” Moreover, they [were the ones who] set up the divisions for singing. Now the Levites would stand on their platform and sing before the One who spoke for the world to come into being. See the love with which the Holy One, blessed be He, loved the Levites. So from the beginning the Holy One, blessed be He, chose them to serve Him. Therefore, the Holy One, blessed be He, said to Moses, “The Levites are extremely dear to Me. Take them in My name for a position of authority.” From where is it shown? From what they read on the matter (in Numb. 8:6), “Take the Levites.”

(Numb. 8:5-6:) THEN THE LORD SPOKE <UNTO MOSES SAYING>: TAKE THE LEVITES. Let our master instruct us: How many strings were on the harp which the Levites played?³²Tanh. Numb. 3:7; Numb. R. 15:11} Thus did R. Judah teach:³³T‘Arakh. 2:7; ‘Arakh. 13b. There were seven (shB') strings on that harp, as stated (in Ps. 16:11): IN YOUR PRESENCE THERE IS FULLNESS (rt.: SB')³⁴Since the S here is a Hebrew sin in the unpointed text SB‘ is identical with ShB‘. OF JOY. Do not read <the word pointed as> sova' ("fullness") but <as> sheva' ("seven"). So also did David say (in Ps. 119:164): WITH SEVEN A DAY DO I PRAISE YOU.³⁵M. Pss. 81:3; PR 21:1. A more traditional translation of Ps. 119:164 would read: SEVEN TIMES A DAY DO I PRAISE YOU. Moreover, in the days of the Messiah it will be made with eight <strings>. Therefore David has stated concerning the instrumental music (in Ps. 6:1): FOR THE LEADER; WITH INSTRUMENTAL MUSIC ON THE EIGHT-STRINGED HARP. Furthermore in the age to come it will be made of ten <strings> as stated {SING TO GOD A NEW SONG…. }³⁶No Psalm has exactly these words but SING TO THE LORD A NEW SONG…. appears in Pss. 96:1; 98:1; and 149:1; as well as in Is. 42:10. [(in Ps. 144:9): O GOD, LET ME SING TO YOU A NEW SONG; LET ME PLAY FOR YOU ON A TEN-STRINGED HARP.] And who ordained them? Samuel and David. It is so stated (in I Chron. 9:22): DAVID AND SAMUEL THE SEER ORDAINED THEM IN THEIR OFFICE OF TRUST. Moreover, they <were the ones who> set up the divisions for singing. Now the Levites would stand on their platform and sing before the one who spoke for the world to come into being. See the love with which the Holy One loved the Levites. So from the beginning the Holy One chose them to serve him. Therefore, the Holy One said to Moses. Levites are extremely dear to me. Take them in my name for a position of authority. {Thus it is stated:} [From where is it shown? From what they read on the matter] (in Numb. 8:6): TAKE THE LEVITES.