The Rebbe taught this melody, to the words from the Yom Kippur services, on Simchas Torah 5717 (1956).
The Rebbe explained that this song encapsulates the bond we all need to feel with each other, as we are all the children of G‑d. We need to treat our fellows as brothers, and the ultimate love between brothers is when there are no strings attached.
In one sense, this song reflects introspective self-assessment and penitence, as well as supplication and invocation to G-d. In another sense, it expresses resolution and fortitude of the spirit, in the hope that G-d will indeed have compassion on his children.
כִּי אָנוּ עַמֶּךָ וְאַתָּה אֱלֹקינוּ. אָנוּ בָנֶיךָ וְאַתָּה אָבִינוּ
For we are Your people, and You are our G‑d; We are Your children, and You are our Father. (Yom Kippur liturgy)