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Many people customarily wear masks and costumes on Purim. Even though there is no source for this in the writings of the Sages, many explanations have been offered for the custom. Here are a few of them:
First, dressing up in costume can be entertaining and make people laugh. Additionally, when people dress differently from their norm, it allows them to relax, be happy, and express their love for their friends. Furthermore, in general, the fact everyone dresses differently serves to separate people. Changing our external appearance on Purim breaks down the barriers between us and increases unity. Finally, by wearing costumes, we become aware of the degree to which we are influenced by external elements. As a result, we can focus more on the internal elements, revealed on Purim.
