"Every person - comensurate with his aspect of kingship - is the equivalent of a watchman." (Rabbi Nachman of Breslov, Likutey Moharan I, 56)
Comment: The kingship is the concept of authority that a person can have on others (parents on their children, a rabbi on his students ...). This kingship shall be used for one purpose: to reveal a Kingship of a higher level, that is to say Hashem's Kingship.
When the Creator put us in a position to be heard by other individuals, this is our test: will we use that authority for our own benefit or to reveal G-d's Glory? It is by trying to bring people around us closer to Hashem that we fulfill our role.
We are never judged on the outcome of our action. If the person to whom we have shown, taught or advised the right path takes another, it is his responsibility. The only thing the Creator ask us is to deliver the message of truth: the one taught by the Torah.