Eliyahu is commanded to effect a changeover in leadership. Just like Moshe, earlier on, Eliyahu is commanded to appoint the prophet who will take his place. Just as Yehoshua served Moshe, Elisha is likewise chosen because of his service to Eliyahu. Reliance on the charisma of the leader is no better than relying on one-time impressive events. The permanent work continues and is not dependent on special, outstanding leadership.
Continuity relies on continuing conscientiousness, regardless of the situation.
Therefore, we are given the mitzva of hakhel, to take place once every seven years. This, however, is not sufficient, as we learn from both Har Sinai and Har Carmel.