What should we do in order to save ourselves from harsh decrees? We must unite. Exile leads us to assimilate among the nations, but the nations’ hatred of us makes us come together as one, and this unity brings about redemption.

The verse states: “One nation that is scattered and dispersed among the peoples” (Esther 3:8). Indeed, as a result of exile and of being assimilated among the nations, the Jewish people are unable to unite properly…. But in truth, every act of Heaven is certainly for the good, for as a result of the fact that [the Jews] attended the feast of Ahashverosh [which, according to the Sages, was the spiritual reason for the decree of annihilation], and associated with wicked people, they were unable to unite [with one another].

Unity brings salvation:

But afterward, the hatred that made the nations decide to destroy them was itself the cause of salvation, as they became [our] enemies and the Jewish people united [out of fear, due to the decree], as it is written: “Assemble all the Jews” (Esther 4:16), and it is written that they “assembled and defended themselves” (Esther 9:16). Therefore, the basic mitzva of megilla is [that it should be read] in the presence of ten [that is, a minyan, the minimum quorum for public prayer]: “Each and every family” (Esther 9:28), indicating that the primary salvation occurred because the Jewish people gathered together to become united. (Rabbi Yehuda Aryeh Leib Alter, Sefat Emet, Purim 5653)

The mitzvot of Purim of mishlo’ah manot and gifts to the poor reveal the importance of unity among the Jewish people:

This is found throughout the megilla. When the Jews were endeavoring to emerge victorious, it is written: “Go, assemble all the Jews” (Esther 4:16), and: “The Jews assembled” (Esther 9:2), and all this is because when Israel is one nation, then God, who is One, is with them, and this is how they defeat Haman and his progeny, who signify the opposite of God’s oneness. Therefore, specifically on Purim, this is the mitzva: “Sending portions one to another, and gifts to the poor” (Esther 9:22), because the basis of these mitzvot is the fact that Israel is one nation, to a greater extent than are all the other nations. (Maharal, Or Ĥadash, Esther 9:22)