In the laws of Hakhel in Hilchos Chagigah, the Rambam writes that “Gerim who are unable to understand the words of the Torah being read by the king, should prepare their hearts and direct their ears to hear, with fear, awe and seriousness just like the day on which the Torah was given”.
The Acharonim elaborate on this idea, explaining how the Mitzvah of Hakhel was a type of re-creation and re-experiencing of the Giving of the Torah and our commitment to the acceptance of Torah and fulfillment of the Mitzvos.
This is reflected in a number of details of Hakhel;. the king would read the Torah as the Shaliach of Hashem, just as we heard Hashem’s voice at Har Sinai. The king stood on a wooden Bimah, and elevated platform like Har Sinai. The entire Jewish people, men, women and children had to be present at Hakhel, just as they were at Har Sinai.
From the Pasuk ויחן שם ישראל, our sages derive that at Har Sinai the Jewish people camped in absolute unity and that this was a pre-requisite for Matan Torah. Unity is a key theme of the Mitzvah of Hakhel.