"A Jew by the name of Mordechai lived in the Capitol city of Shushan." (2:5)
When the Megillah is read in public, it is a custom for everyone to say this pasuk aloud. What is special about this pasuk?
In the Megillah we find the expression Shushan Habirah (Shushan the Capitol) ten times, and nine times Ha'ir Shushan - "The City of Shushan" or just plain "Shushan." Obviously this is intentional. Why the distinction?
Shushan Habirah was the capitol of Achashveirosh's kingdom.
Near it was a suburb known also as "Shushan." It was forbidden for Jews to live in the capitol city, but they were permitted to live in the city of Shushan. Therefore, when the Megillah talks about Achashveirosh or the issuing of decrees, Shushan Habirah is mentioned. Whenever the Megillah talks about the Jewish people, Ha'ir Shushan is mentioned.
By Divine Providence, Mordechai was the only Jew who happened to be living in the capitol. Thanks to this, he had access to the King's palace and was able to overhear the conversation of Bigtan and Teresh, which eventually brought about the downfall of Haman and the miracle of Purim.
According to Rabbi Yehudah (Gemara Megillah 19a), the reading of the Megillah in public should begin with this pasuk because it portrays the strength and prominence of Mordechai. The above-mentioned explanation offers an insight into Rabbi Yehudah's opinion.
"And when her father and mother had died, Mordechai adopted her as his daughter." (2:7)
The Gemara (Megillah 13a) says, "read not 'lebat' -- 'a daughter' but 'lebayit' -- 'a wife,' " [lit. "a home"]. Instead of alluding, why doesn't it say "bayit" explicitly?
The Gemara (Ketubot 59b) says that the purpose and desire of a women is in three things. 1) "Bonim" -- children. 2) "Yofi" -- beauty. 3) "Tachshitim" -- jewelry.
The acronym of these three is the word "Bayit". The Gemara (Megillah 13a) says Esther was of greenish complexion (like a myrtle). However, G-d endowed her with a touch of grace -- kindness. This made her appear beautiful in the eyes of the people and Achashveirosh (Rashi).
Consequently, of the three characteristics which make up the uniqueness of the women she was lacking the "yud" which stands for "yofi" beauty. Hence, in consideration of the two feminine qualities the Megillah refers to her relationship with Mordechai as "Bat" -- "a daughter," but our sages tell us that she was really "Bayit" -- a full fledged wife.
"Bigtan and Teresh became angry... and sought to lay hand on King Achashveirosh: The plot became known to Mordechai, who told it to Queen Esther; and Esther informed the King in Mordechai's name... After these things King Achashveirosh promoted Haman." (2:21-22, 3:1)
Why was Haman promoted and not Mordechai, who provided the information?
Achashveirosh figured that if Mordechai was in fact concerned about his well-being, rather than telling Esther about the plotted assassination, he should have come directly to him. Therefore, he was in doubt as to Mordechai's true intentions.
However, Esther, who revealed the secret plot to him, was indeed loyal and deserving of a reward. Since Esther as Queen had the maximum any woman could desire, Achashveirosh was in dilemma: what more could he give her?
Achashveirosh concluded that Esther esteemed Haman very highly, because upon his advice Vashti was killed, thus making it possible for her to become Queen. Assuming Haman to be Esthers trusted ally, Achashveirosh rewarded Esther by promoting him.