One of the Korbanos discussed is the sin-offering of the Nassi - the leader of the Jewish people. His Korban is introduced with the words אשר נשיא יחטא “if the Nassi will sin”.
Our sages explain that the word אשר also means fortunate. They explain that the Torah is teaching us that “fortunate is the generation in which the Nassi takes to heart to bring a sacrifice for their unintentional sin and certainly they will regret an intentional wrongdoing”.
The Mitzvah of the Hakhel reading had to be performed by the King. According to many authorities, even if there is no one who carries the title of king, the Mitzvah applies to the Nassi, the primary leader of the Jewish people.
One of the reasons why the reading had to be done by the king, is because the people would see how even the ultimate authority figure humbled himself to the word of Hashem and was bound to observe the Mitzvos. From this the people would deduce how much more so they must humble themselves and submit themselves to follow the word of Hashem.