Parshat שופטים speaks about the importance of listening to the words of a true profit. It describes how we are to see the signs revealing that he is chosen by G-d to deliver His message to the people.
Rabbi Soloveitchik raises a question regarding the prophecy of Moshe Rabbeinu. If Moshe transmitted the entire Torah, then every Mitzva not observed, would also carry with it the violation of not listening to the prophet.
The answer proves that Moshe stood alone as the greatest of all profits. He, alone, had his teachings considered actual Torah. Things learned from other prophets are defined as דברי קבלה or דברי מסורת. We are obliged to follow these teachings as well, but they do not have the status of the teachings of Moshe Rabbeinu.