Moses first sent messengers to Sichon the king of the Amorites to ask him, on behalf of Israel, to let them pass peacefully through his land.
On behalf of Israel: The fact that the Torah says that Moses sent messengers to Edom but Israel sent messengers to Sichon, even though in both cases Moses sent the messengers on behalf of all Israel, teaches us that Moses and Israel are essentially equivalent.
The true Jewish leader does not just represent the people, he is one with them in essence. His affairs are not compartmentalized into his private and public lives. He is a public servant to his very core. Therefore, anything he does is considered to have been done by the entire people.
The true Jewish leader's total identification with the people and selfless devotion to them makes him the conduit through which G-d provides all their material and spiritual needs. Therefore, not only is he one with them: they are one with him. As such, they can rise to his perspective on reality and share his Divine consciousness and inspired life, even if they have not yet refined themselves enough to be worthy of these on their own.
From the Kehot Chumash Bemidbar