This tune comes from an old freiliche niggun referred to as the “Simchas Torah Niggun”, and the words are what we write and wish fellow Yidden during the month of Elul. The two were combined at Gan Yisroel Detroit in the summer of תשמ”ח (1988).
On Gimmel Elul of that year, the campers arrived back in New York. Some of them went to daven Maariv at the Rebbe's house. After davening, the campers said Yechi and began singing the new niggun. The Rebbe looked at them with a glowing face and encouraged the niggun.
The Rebbe went upstairs and shortly afterwards - to everyone’s surprise! - the Rebbe came back down and said a sicha for the campers, and handed out dollars.
In the sicha, the Rebbe explained that since it’s a minhag Yisroel to כְּתִיבָה וַחֲתִימָה טוֹבָה (May we be inscribed and sealed [in Hashem’s books] for a good, sweet year), wish each other “כְּתִיבָה וַחֲתִימָה טוֹבָה” throughout the month of Elul, the wish will certainly come true. This bracha has a real effect, and the one who is blessed actually gets inscribed and sealed for good—especially when we are confident in the power of the bracha.
