Tafsiran Bilangan 4:47: Rashi, Rabbeinu Bahya, Siftei Chakhamim & Rav Hirsch

עבדת עבדה THE SERVICE OF THE MINISTRY — (lit., a service of a service). This is the song of the Levites with accompaniment of cymbals and harps, this being the service attached to another service (the sacrificial service) (Arakhin 11a).

לעבוד עבודת עבודה, “to perform the work of service.” This is a reference to the song which in itself was a service to support another “service,” namely the sacrificial offerings (Erchin 11). This reflects what David said in Psalms 100,5: “serve the Lord in joy.” We have a clear verse that the offerings were accompanied by song in Chronicles Ii 35,15: “the Asaphite singers were at their stations, by command of David and Asaph and Heman and Jeduthun, the seer of the king; they did not have to leave their tasks.” The “song” referred to was accompanied by music played with harps and percussion instruments. They used to sing the praises of the Lord at the times the daily public sacrifices were being offered on the Altar.
Our sages (Erchin 13) discuss the details of the musical instruments such as the number of strings on the harp (lyre) being seven. They base this on Psalms 16,11 שובע שמחות את פניך, “In Your presence is perfect joy.” They suggest that instead of reading the word for “perfect” as sovea, it should be read as sheva, “seven,” [same spelling as letters without vowels. Ed.] According to tradition, when the Messiah will come the music played at the sacrificial offerings will be on an instrument with eight instead of seven strings. This is alluded to in Psalm 12,1 which commences with the words: “on the eight-stringed instrument.” In a still more distant period we envision a harp featuring ten strings as alluded to in Psalms 33,2 as well as 92,4. All of these details are discussed at the end of the second chapter of Erchin. [The relevance of these somewhat peripheral-sounding discussions is that our present universe is perceived as being based on the seven fixed stars, planets of pre-Copernicus astronomical principles, Ed.].
It is presumed that the general supervision exercised by G’d over all of mankind once the messianic age arrives will be increased to eight such planets. At a still later period, the period perceived as “the world to come” (in terms of resurrection of the dead), the world will enjoy supervision by G’d based on ten planets assigned that task.
You should be aware that the entire subject of song being offered during the offering of the public sacrifices has not been spelled out anywhere until the time of David.

The number of Levites (of whom Scripture tells specifically as singing hymns) is eight. They were: אסף, הימן, ידותן ,איתן האזרחי,; this makes four. Add Levi, who is referred to here as בן “son;” this makes five; then there is the one called על הגיתית, a reference to the family of Gattit a song offered by that family who hosted the Holy Ark. (compare Chronicles I 13,13). This gives us six. Add the sons of Korach; this makes seven. Finally, there are the “sons” of Moses giving us a grand total of eight such “singers,” or better: “composers of songs and hymns” who were all Levites. These eight people between them used eight musical instruments. The instruments are known as:
1) נגינות (Psalms. 4,1).
2) מחלת, (Psalms. 53,1).
3) עלמות שיר (Psalms. 46,1).
4) משאת (Chronicles I 15,22).
5) נחילות (Psalms .5,1).
6) שושנים, (Psalms. 45,1).
7) גתית, (Psalms. 8,1).
8) שמינית, (Psalms 6,1).

ועבדת משא is what it literally implies: AND THE SERVICE OF CARRYING.