While we know her as Esther, she was also known as Hadassah. Hadassah means myrtle, a name used in the Torah to refer to the righteous. The myrtle is a paradoxical plant—it has a sweet fragrance and a bitter taste. Esther was sweet to Mordechai and bitter to Haman. She balanced kindness and severity.
Her name Esther suggests concealment (hester), alluding to her hiding her Jewish identity from the king. Additionally, the non-Jews called her Istahar which means moon, and praised her for being beautiful like the moon.
Esther also alludes to the fact that G-d's face was hidden during her time. As the Midrash teaches, if the moon does not appear in the sky at night, the world is so dark that a man cannot walk about even within the city. But as soon as the moon appears in the sky, all rejoice and walk about. Ss it was in the dark days of Achashverosh, who decreed that Israel should be destroyed, slain and made to perish. But Esther, who is compared to the moon, came and brought light to Israel, as it says: The Jews had light and gladness, and joy and honor.
Esther’s two names represent two possible states of the Jewish people. During times of spiritual prosperity, when G-d’s presence is obvious, we are easily inspired to be righteous. We are then called Hadassah, which alludes to the righteous. Then there are times of spiritual poverty and exile, when G-d’s face is hidden. In those times, we are called Esther.
Ironically, in the hiddenness of exile, we can connect with G-d in an even deeper way. In the darkness, the soul’s deepest bond with G-d is revealed. This is why the Megillah refers to her as Esther, not Hadassah, because Esther captures the predicament, and the great promise, of the Jews in exile. As the Megillah tells us, Hadassah—she is Esther. This means that even in the difficult times, when we seemingly have drifted from G-d, the truth is that beneath the facade of concealment shines the righteousness of “Hadassah” and the ability to give our very lives for G-d.
--Eishet Chayil