Likutei Moharan, Part II 31:1/ליקוטי מוהר"ן·תנינא ל״א:א׳

1From the song [he sings] it is possible to tell if a person has accepted upon himself the yoke of Torah.

2This is the import of “on their shoulder yisa’u (they did carry)” (Numbers 7:9). Concerning this our Sages, of blessed memory, expounded: yiSA’U is nothing other than song, as is stated (Psalms 81:3), “SA’U (Raise up) a song and sound a timbrel” (Arakhin 11a). This verse appears in connection with the undertakings of the Kehatites, who hoisted the Ark onto their shoulders—this being the concept of the yoke of Torah.