Esther's preeminent role is highlighted in the very name of the Megillah, the Biblical Scroll which recounts the Purim narrative. 
It is not called "Megillas Mordechai" or "Megillas Mordechai and Esther" or even "Megillas Esther and Mordechai." It is called simply "Megillas Esther."
Though it was indisputably Esther who actually moved Achashverosh to act, Mordechai also played a role in the salvation. Indeed, the Megillah testifies that he was the dominant force behind Esther.
In fact, she is first introduced in the Megillah in terms of her relationship to Mordechai:  "He had brought up Hadassah, that is, Esther, his uncle's daughter."
Her every action was based on Mordechai's advice:  "Esther would carry out the bidding of Mordechai."
Her supreme moment, when she was to go to the King to plead for her people, took place only at Mordechai's instigation and virtual command.
So reluctant was she to go that Mordechai had to speak harshly:  "If you remain silent at this time, relief and deliverance shall arise for the Jews from another place, while you and your father's house shall perish. And who knows whether you did not come to royal estate for just such a time as this?"
Since Mordechai thus played a critical role not only in Esther's life but also in the national crisis, should not the Megillah, which narrates the events of the danger and the subsequent salvation, be named after both of the chief participants in the salvation, Esther and Mordechai?
This question can be resolved by seeing Mordechai and Esther not only as individuals, but also as personifications of the Torah and the Jewish people, respectively.
Our Sages affirm:  "Mordechai in his generation was equal to Moshe in his generation. ... Just as Moshe taught the Torah to Israel,... so did Mordechai."
Esther, the Talmud teaches,  was called Hadassah "after the righteous who are called myrtles (hadas)" - and  "Your people are all righteous."
On one level, the Torah, personified in the Megillah by Mordechai, transcends Israel, personified by Esther, for Israel must follow the Torah's directives. In the words of the Megillah,  "Esther (Israel) would carry out the bidding of Mordechai (the Torah)." Indeed, the Torah is the medium which brings to light the unique distinction of Jews.
On the other hand, once the distinctive qualities of the Jewish people have been revealed by means of their identification with the Torah, their innate superiority blazes forth, and Israel is seen to be loftier even than the Torah. As our Sages have said,  the Divine intent of creating Israel came to mind, so to speak, before anything else, even before the Torah.
In words of a different flavor:
The Baal Shem Tov compares the Jewish people to a land filled with precious resources, as in the verse,  "You shall be a land of delight."
Every Jew possesses valuable qualities and virtues; but these treasures are buried deep within him, and persistent toil is needed to bring them to light - just as one must dig deep to uncover the precious metals and gems in the earth. Once the concealing strata have been removed, a Jew's innate qualities shine forth.
The same may be said of Mordechai and Esther as individuals, in their roles in the story of Purim.
Mordechai, it is true, had to persuade Esther to do her part in removing the decree against the Jews. But Mordechai did not need to effect any basic change in her.
His function was only to reveal her innate qualities, to allow her real self to surface. And once he succeeded in doing this, Esther set out on her mission with her own strength, impelled by her own convictions. At this point, she became the direct cause of the miracle.
For in her true and innate state which was now revealed, Esther stood on a higher rung than Mordechai. It was she who now took the initiative to tell Mordechai,  "Go, gather all the Jews to be found in Shushan, and fast for me." And it was Esther who convinced the Sages of her time to include the Megillah as one of the sacred writings of the Tanach. 
The miracle of Purim thus came about through Esther's own innate qualities, albeit after Mordechai revealed them. Moreover, those qualities were infinitely superior to Mordechai's, just as Jewry in essence is infinitely loftier than the Torah. For these reasons, Megillas Esther is named solely after her.
The Baal Shem Tov offered a unique interpretation of the mishnah which states, 
"One who reads the Megillah backwards has not discharged his obligation."
That is to say:
If one reads the Megillah thinking that the events related in it happened only in the past ("backwards") and are not relevant today, he has missed the entire point of the reading - to learn how a Jew should conduct himself at all times, now as in the past.
Hence the importance of noting the name of the Megillah, which, as explained above, emphasizes the greatness of a Jewish woman.
Just as our frequent reiteration of the distinctive qualities of Jews is not chauvinism, but is intended to highlight the obligations of Jewry, so the purpose of talking of the greatness of Jewish women is to stress their weighty responsibilities.
Every Jewish woman is the mainstay of her home, who sets the tone and spirit of the entire household.
In particular, it is the woman who bears the responsibility of rearing her children in the traditions of Torah and Judaism, ensuring that they live every aspect of life as Torah Jews.
It is the woman, the constant presence in the home, who has the task of ensuring that the home be pure and sanctified, suffused with the light of Torah and mitzvos.
In particular, her task is to buttress the three pillars of the Jewish home: the kashrus of the food consumed, the kindling of the Shabbos and Yom-Tov lights, and the bringing of children into the world in the spirit of the laws of family purity,  together with their subsequent upbringing.
The characteristic qualities of the Jewish woman recall the verse in the Megillah, 
"For the Jews there was orah ('light')," which alludes to the Torah. 
Now "or", which also means "light", refers to the Written Torah.
Why does the Megillah choose to refer to the Torah as orah (using the feminine form of that word), which refers to the Oral Torah? G-d's Will is expressed in both the Written and the Oral Torah.
However, as the Alter Rebbe writes,  "the Supreme Will as vested in the 613 commandments of the Written Torah, is hidden and covered, secreted and concealed. It is manifest only in the Oral Torah."
The Written Torah, for example, says of the mitzvah of tefillin that  "You shall bind them as a sign on your arm, and they shall be for frontlets between your eyes."
What exactly this instruction means, and just how it is to be fulfilled, remains obscure until it is clarified in the Oral Torah.
In the metaphorical language of the Kabbalah, the Oral Law fulfills the characteristically feminine function of unfolding each seminal teaching and nurturing it into full flower in all its tangible detail.
It was therefore the Oral Torah, whose laws enable Jews to fulfill the Divine Will on a practical level, that was Haman's chief target. 
Hence, when his decree was frustrated, "for the Jews there was orah" - the light radiated by the Oral Torah, against which his decree was primarily directed.
Purim thus highlights action, the translation of the Supreme Will into actual practice, and it is the Oral Torah which enables a Jew to do this through the observance of the commandments.
This, then, is the connection of the Oral Torah to the name of the Megillah - not Megillas Mordechai or Megillas Mordechai and Esther, but simply Megillas Esther; and in the Megillah the Torah is called only orah, using the feminine form of the noun, and not "or", or both "or" and orah.
"These days," the Megillah assures us,  "are recalled and observed in every generation."
In our days, too, the events of Purim again come to life, particularly since Purim teaches an evergreen lesson.
As the above verse goes on to say, "These days of Purim shall never cease among the Jews, and their remembrance shall never perish from their descendants."
In the spirit of the above, may it be G-d's will that the Week of the Jewish Woman, whose purpose is to inspire and encourage Jewish women in their faith, and which is being observed at this Purim season, will 
"benefit themselves and benefit the world."
May the deeds of Jewish women illumine the whole world with the light of Torah and mitzvos, so that even in these last days of exile G-dliness will be revealed in the world - just as in the era of the Redemption, when  "The glory of G-d shall be revealed, and all flesh together shall see that the mouth of G-d has spoken."
- (Back to text) The prime mortal architect of the miracle of Purim was Esther. In the course of this episode, which took place in early Second Temple times, the Jews dispersed throughout the 127 provinces of the Persian Empire were saved from the anti-Semitic designs of Haman, grand vizier to King Achashverosh (Ahasuerus).
Risking her life for her people, Queen Esther braved the King's anger and entreated him to have pity on them. As the Megillah records, she was eminently successful.
The above text summarizes a talk of the Rebbe on Shabbos Parshas Tzav, 13 of Adar II, 5744 , in connection with the Week of the Jewish Woman.
- (Back to text) Esther 2:7.
- (Back to text) Ibid. 2:20.
- (Back to text) Ibid. 4:14.
- (Back to text) Esther Rabbah 6:2.
- (Back to text) Megillah 13a.
- (Back to text) Yeshayahu 60:21.
- (Back to text) Esther 2:20.
- (Back to text) Bereishis Rabbah 1:4.
- (Back to text) Malachi 3:12.
- (Back to text) Esther 4:16.
- (Back to text) Megillah 7a.
- (Back to text) Ibid. 2:1.
- (Back to text) See the essay below entitled "Family Planning."
- (Back to text) Esther 8:16.
- (Back to text) Megillah 16b.
- (Back to text) Tanya - Iggeres HaKodesh, Epistle 29. (See Lessons In Tanya, Vol. V, p. 221.)
- (Back to text) Devarim 6:8.
- (Back to text) Note the charge with which Haman slandered the Jews to Achashverosh ("their laws are different from [those of] every nation"; Esther 3:8).
- (Back to text) Esther 9:28.
- (Back to text) Cf. Sanhedrin 71b.
- (Back to text) Yeshayahu 40:5.