The Jewish People have never had a Prophet or a Leader as great as Moshe Rabeinu.
The Jewish People were in utter chaos after the Golden Calf. G-d came close to annihilating every one of us (Parshat Ki Tisa (32:10) "And now desist from me! Let my anger burn against them and I shall annihilate them; and I shall make you a great nation"). Moshe assembled the Children of Israel on the day after Yom Kippur (according to Rashi) as a true Leader and brought Unity to the existing chaos.
"And Moshe assembled the entire assembly ("Adat") of the Children of Israel and said to them: "These are the things that Hashem commanded to do them" (35:1). The Zohar says that the word "Adat" means the Erev Rav were excluded and left out of making the Mishkan since they were responsible for the Golden Calf. Rabbi Moshe David Vali says the Erev Rav were like a Leopard who could not change his spots and hence were excluded.
The Chida says that the word "Vayakhel" means purification since the Gematria is 151 equal to the numerical value of the word "Mikveh" which purifies. The Kli Yakar says that since all Jews ask Mechila of each other before Yom Kippur, the Jewish People were United as a result at this point. Unity of the Jewish People is the ultimate goal.
The Torah cannot be fulfilled in its entirety until the Jewish People are United. The 613 Mitzvot depend upon each and every Jew doing his or her part. Har Sinai occurred at the moment the Jewish People were most United-our "finest hour". As I wrote previously Har Sinai caused Unity and Unity brought about Har Sinai.
Vayakhel is an attempt to recreate the Har Sinai Experience. Unity is crucial to attaining and accomplishing this experience. Vayakhel according to the Chida was to reunite the Jews for positive to contrast the negative of the Golden Calf. Rav Gedalia Schorr says each step of the way was to counteract what mistakes were made at the Eigel. The gold used in making the Mishkan was to counteract the gold used in the Eigel. The Chida says that when Jews assemble as they did in Vayakhel, or in a Minyan for that matter, as a Tzibbur, Hashem looks at the individual completely differently.
Hashem judges individuals differently when they are part of a Tzibbur. The Baal Shem Tov says that all prayers, all Mitzvot "For the sake of the unification of the Holy One Blessed Be he" refers to the Unity of the Jewish People when the Jewish People are together in a Tzibbur then Hashem is sanctified. This is the lesson of Vayakhel. This is what Moshe was doing in bringing back the Jews to the proper Derech. Rav Gedalia Schorr says without Achdut (Unity) we can't fulfill the whole Torah. It requires a Kehilla. Individuals have to be part of the whole.
The Chida says that the day after Yom Kippur was chosen because just as Moshe was the most humble of all men, he was trying to teach humility to the Jewish People. The day after Yom Kippur is when the Jew is at his or her humblest state. Parshat Vayakhel was Moshe's attempt at teaching Humility. Torah cannot be fully appreciated without humility. This is essential. The Eigel experience was the opposite. Moshe Rabeinu brought us back from the Brink. Unity and Humility are what he taught us. This is a lesson we can never afford to forget. Shabbat Shalom.