לַמְנַצֵּ֣חַ בִּ֭נְגִינוֹת עַֽל־הַשְּׁמִינִ֗ית מִזְמ֥וֹר לְדָוִֽד
lamnatzeyach bingiynos ʿal–hashemiyniys mizmor ledovid
For the leader; with instrumental music on the sheminith. A psalm of David.
1.....(6.1)
For the leader; with instrumental music on the sheminith.
Thinking of circumcision, David said, I will compose a Psalm concerning it, For the leader, with string music, on the eighth (Sheminith) that is, on the eighth testimony, circumcision, which is performed on the eighth day.
2.....(6.2)
For the leader; with instrumental music on the sheminith.
The phrase on the Shiminith alludes to the fourth dispersions of Israel under eight kingdoms..., Babylon, Chaldaea, Media, Persia, Greece, Macedon, Ishmael and Edom.
1.
...on the sheminith:
A harp of eight strings, known as sheminith
1.
For the leader; with instrumental music on the sheminith.
There are some (Targum ad loc.) who interpret Sheminith as a lyre which had eight strings, and the Psalm as being recited to the accompaniment of this music.
The Haggadic interpretation (Babli, Menahoth 43 b) (applies it) to circumcision, which was performed on the eighth day, but this is far-fetched.
This Psalm possibly was uttered by David with reference to his sickness; it is also possible likewise that it was uttered in the language of anyone crushed by sickness, for David composed many of the Psalms which combine prayer and supplication that they might be suitable for any suppliant; and such, I think, is the case in this Psalm.
And some say (Ibn Ezra ad loc.) that it was uttered with reference to the Exile, for Israel in exile was like those who are sick and crushed.
1.
For the leader; ... on the sheminith.
A similar title can be found only in one other place, that is, Psalm 12. In both psalms the Psalmist seeks to raise the human spirit from a state of utter despair. Both psalms stress how futile it is to expect help from men. This realization is then logically followed by an affirmation of confidence that God would intervene with His saving power at the hour of utmost need. The only difference between the contents of these two psalms is that while Psalm 6 speaks of one individual's state of utter despair, Psalm 12 deals with the utter depravi ty of human society as a whole.
In Arachin 13b, the phrase "on the sheminith" is interpreted to mean - “on the eighth string”.
It is explained there that the harp ordinarily used in the Temple had only seven strings, while the one intended for the Messianic era had eight, and the instrument representing the form the world will take in the future had ten strings.
The numerals 7 and 8 have significance in Jewish literature
The number 7 always indicates the element of the Divine connected with the physical world of the creation, God in covenant with His world and the world in communion with God. This is shown typically in the words [שבת] (Sabbath) and [שבועה] (The oath).
The number 8, on the other hand, points to the Eighth Work of God, namely the institution appointed in world history by God for the regaining of the forfeited “Sabbath” and the lost communion with Him. It is the Lord alone Who loosens the bonds of death and guilt and is ready at all times to grant new life and a new future with His call to action and His omnipotent grace to those who seek it.
Therefore, the institution of Milah on the eighth day, which teaches us that to free ourselves from the fetters of the sensual world is a basic prerequisite for our covenant with God, bears the symbol of the number eight. In general, the number 8 is found as a symbol in Divine law wherever that Law teaches us to strive, in and through God, for freedom from those constraints imposed upon man by sensuality and the amenities of human society.
Hence those hymns of the Temple praising the presence of God on earth and the union with God of all things earthly are played on the harp of seven strings. The song of the days of the Messiah, when final redemption will come to all, sounds forth from the instrument of eight strings. The harp of ten strings, however, is reserved for the song which shall rise on that day when the world that is to be will be united in one harmonious whole.