it becomes small

 If you say that the Torah is big, but then submit yourself to someone who is familiar with only a small piece of it, then it effectively becomes small. Now if that person knows more than you or something that you don't, he can be helpful, but there's a difference between someone who is helpful to you and someone you look at as everything. Every soul is different. How can one person encompass another? Maybe it's different with the handful of Torah giants, particularly of prior generations. But the average person has access only to the average rabbi, who is not capable of encompassing other people. Today, many people think of a rav as a master. He is in charge of your decisions and your thoughts. You have to filter everything through him. And they are obsessed with this idea of "having a rav." It's the first question they ask you. "Do you have a rav?" I have heard more than one rabbi say to young women, "If he doesn't have a rav (a master) forget him." So this shomer mitzvos young man is suddenly discredited, outcast, and rejected because he doesn't have this one person to rule over him. It's a cynical notion. But it might be something worse. It might be a way of taking people away from the Torah. If every young man has to obey men who know a sliver of Torah, then you have torn them away from Torah and handed them over to conventional constructs. And if, as it is said, most rabbis in the era before moshiach are eruv rav, then you have handed him to erev rav. He's not even allowed to say that something violates the Tanach. No, you must listen to your rav, not to the Tanach, they'll say. Read this as, you must listen to the erev rav.