Both the Chassidim and the Mitnagdim are mistaken. The Mitnagdim are mistaken in that they believe that they don't need a Rebbe. The Chassidim are mistaken in that they believe that they have a Rebbe. - Reb Yisrael Lipkin of SalantReb Yisrael is teaching us two very important lessons in his own inimitable fashion. When it comes to continuous growth in our character refinement and devotions, it is not enough to just sit and learn (although that obviously goes a long way in the right direction), but rather, one must attach himself to a master, a tzaddik around whom a group of people with like-minded goals in spiritual improvement can rally around. This tzaddik should be able to recognize the particular strengths of each individual, to help that individual actualize his potential. But cleaving to a tzaddik cannot be a mere cultural thing, either. It is very easy to fall into a false sense of security through mere association, but that is not the essential nature of the relationship. One must seek out the tzaddik, question him and engage him; the relationship between tzaddik and pupil is mutually beneficial for true growth.
UPDATE: For more on this idea, see this post by the wonderful Reb Ally.