Hakhel was dramatic and unifying, emphasizing our national identity as a people of the Torah. The Chumash associates this gathering with Sukkos and Shemitta.
Interestingly, Chazal tell us that it is to be performed on Chol Hamoed following the Shemitta year, and not on the the Shemitta year itself.
Chatam Sofer explains that the Hakhel is especially appropriate following Shmitta. The farmer who didn’t have to plough and plant all year would dedicate himself to spiritual pursuits. Following this year, we would experience the Holy days of awe, Yom Kippur’s purification, the super holy Sukkot where we dwell in His tent, we finally merit this awesome assemblage.
In Chassidus there is an emphasis on “hachana”, preparation, for Mitzvot.
The Rebbe ‘Shem Mishmuel”, emphasizes that year-long preparation for Hakhel outweighs the advantage of commencing the Shemitta year with the push of Hakhel.
Meshech Chochma has a different twist. After refraining from work for a full year, the farmer would be eager to start working full-force. Still, he must refrain a bit more to hearken the word of Hashem.
The Hakhel was certainly a tremendous Chizuk for all who experienced it, reminiscent of Ma’amad Har Sinai. This national culmination and preparation is sorely missed, and we are looking forward to experiencing it again במהרה בימינו.