Before a Chossid enters the Rebbe’s chamber for Yechidus, where he will reveal to him what bothers his Neshomah and request advice in his Avodas Hashem, he must prepare himself. This is done by purifying oneself and making a thorough ‘Cheshbon Ha’nefesh’ through which he arouses his deepest feelings for Teshuvah and seeks to ascend to a higher, more spiritual life. It is during this lengthy contemplation that a melody escapes his lips, a song full of feeling which express the present situation of his Neshomah.
It is with this idea that Reb Shmuel Zalmanov, in his introduction to this niggun in Sefer Haniggunim, describes the feelings expressed in this song. Indeed, if you pays close attention then you will be able to hear how the notes climb higher and higher and then descend, up and down, up and down, accompanying the pre-Yechidus meditation, preparing to stand in front of the Rebbe’s holy presence.
It seems that there are many “niggunei Yechidus”, for every Chossid would have “his” niggun that he would sing, expressing his own private feelings as he prepared himself to enter the Rebbe’s room for Yechidus. The one in Sefer Haniggunim is from Reb Shlomo Tchasniker and to date is the only one which is known as “Niggun Ha’yechidus”.
In a letter it states that the Maskil Shimon Ha’kofer wrote to his superiors, the heads of the Haskalah movement, about the different niggunim that Chassidim would sing, one of them being niggun Ha’yechidus.