Moshe assembled all the congregation of the Children of Israel, and said to them, "These are the words ..." (Shemos 35:1)
Everyone's eyebrows go up over the emphasis on Moshe's gathering of the people to hear G-d's command, asking, "Why is this night different from all others?" (to borrow the words from the Haggadah). In other words, why doesn't it say that Moshe "gathered the people" in other places that he was told to speak to the Jewish people on behalf of G-d?
The Ohr HaChaim HaKadosh says that, after Moshe came down exuding light at the end of last week's parshah, many from the Jewish people were afraid to approach him. Therefore, Moshe summoned all of them to come before him, to allay their fear--men, women, and children too.
The Ohr HaChaim also says that normally, women and children were not in attendance when Moshe told over G-d's words. However, since the building of the Mishkan was from "gifts of the heart" brought from ALL the Jewish people, the women and children were also asked to be present when Moshe spoke on this topic again.
Another reason for the complete assembling of the entire nation has to do with what Rashi mentions. Rashi says that this parshah begins on the eleventh day of Tishrei, the day after the first Yom Kippur in the history of the Jewish people, and eighty days after the building and destruction of the golden calf. Moshe had since ascended for two more sets of forty days, in order to beg G-d for forgiveness on behalf of the Jewish nation. Apprehensively, every Jewish man, woman, and child waited in the camp below for G-d's verdict. Hence, it was only fitting that all should be convened to hear the good news.
The Ba'al HaTurim adds yet another idea. He says that, since this massive gathering was to teach laws of Shabbos and Yom Tovim, it was also a way to instruct the Jews to gather together on these special days for communal drashos (Torah lectures).
And finally (for now), one more underlying concept behind this anomaly in the Torah may simply be to emphasize the need for Jewish unity. Nothing empowers the Jewish people more than when we rally around the banner of Torah as a unified whole. Fragmented, we become weak and vulnerable to all kinds of anti-Torah currents, as the account of the golden calf proved.
It is amazing how quickly and effectively immorality is able to mobilize followers to do its bidding. This is because it does not take much convincing to satisfy one's more base instincts. However, when it comes to fulfilling man's loftier side--the side of the soul--it is never an easy job; it is not one that tends to go very smoothly (like picking up a link-chain from only one end).
Hence, Shabbos is the mitzvah they were gathered together to learn in this week's parshah. For, Shabbos is the great unifier, integrating the previous unrelated six days of the week and synergizing their efforts and successes. And though national unity, for this moment at least, seems to be a distant dream, we must remember that every little bit of unity counts in this critical effort. G-d cares about Jewish unity, and each of us has to start somewhere.
(Author, lecturer, and scholar Rabbi Pinchas Winston is the director of ThirtySix.org