The following is a brief summary of part of a shiur that I heard this evening. I am unaware of the name of the maggid shiur as he was not identified in the satellite broadcast. I have attempted to reproduce this vort to the best of my ability. Any perceived inconsistencies are the result of my efforts to transcribe the shiur and should not be attributed to the speaker.
In the first sentence of this week's parsha, Moshe brings all the Jews together to tell them about the building of the Mishkan. The Klei Yakar comments that all of the Jews were gathered together for this announcement, because they all had a role in the building of the Mishkan. He further explains that this event occurred on the day after Yom Kippur because the Jews had all been united in their prayers for Yom Kippur and now that unity had been achieved they could work together on building the Tabernacles.
R' Yaakov Kaminetsky explains that when the Jews received the Torah they had been united together. [This can be seen from the use of the words Na'aseh V'Nishma - the singular form that we will do and we will hear]. However during the sin of the golden calf the Jews were all separated to the point that each tribe had its own calf. In order to create the tikkun for the sin of the golden calf through the building of the Mishkan, the Jews first needed to be united again through their Yom Kippur prayers.
R' Shlomo Alkabetz (author of the L'cha Dodi prayer) finds a similarity in the Purim story. When Esther tells Mordechai about her plight she tells him (4:16) to go and bring all the Jews together. This was done to correct the problem that Haman had observed that the Jews were scattered amongst the people or Persia and Media (3:8). The success of bringing together of all the Jews can be seen at the end of the story where it is said that the Jews were organized together (9:2).
We can also see how great the power of Purim is, even greater than Yom Kippur. Before Yom Kippur a person will approach his friend and ask for forgiveness. This can act to mend fissures in a friendship. On the other hand if a person sends shalach manot to someone that he is not friendly with he can create new relationships where there was previously enmity.
We should only see togetherness among the Jewish people.