Rashi writes that the verse stresses that families celebrating Purim should eat and drink together in order for Purim to “never cease.” The Ohel Moshe notes that it would seem from this that Purim would not exist without unity in the family.
The Ibn Ezra explains that this is the case in order for nobody to be able to say “my (family, city, country) wasn’t affected.” All Jews were equally rescued through this miracle.
It is for this reason, explains the Vilna Gaon quoting the Talmud (Megilla 3a) that even Leviim and Kohanim should put aside the Temple service to hear the public reading of Megillas Esther on Purim.
R’ Hutner adds that this injunction pays homage to the fact that Amalek failed to corrupt the Jewish family (see Rashi to Devorim. 25:18).