We are one because we share a single soul, like a single, brilliant sun shining into many bodies. Since the soul is what counts, that makes us essentially one.
That is the meaning of the mitzvah of the Sukkah—a place that encompasses us all equally, rendering us a single whole.
We are also one because none of us are alike. Each of us reflects a different facet of that same soul, each of us with our strengths and our weaknesses, so that we all need one another to be whole and complete.
That is the meaning of the mitzvah of the Lulav, the Etrog, the Hadassim and the Aravot—four very diverse species...